The 30-Second Answer
The Illinois Equal Pay Act (820 ILCS 112/) requires that employees performing substantially similar work receive equal pay regardless of sex or race — and since 2021, Illinois employers with 100 or more employees must obtain an Equal Pay Registration Certificate from the Illinois Department of Labor or face a $10,000 penalty per violation. This is not a soft standard. It is a compliance regime with real enforcement teeth, real disclosure requirements, and a private right of action that allows underpaid employees to sue for the wage difference plus interest, attorney’s fees, and costs.
The Story
Keisha Monroe and Ryan Callahan both worked as senior financial analysts at a suburban Chicago asset management firm in Downers Grove, DuPage County. Same title. Same team. Same clients. Keisha had been there four years; Ryan, two. When Keisha accidentally saw Ryan’s pay stub left on the printer, she discovered he was earning $11,000 more annually than she was. She asked HR why. They said Ryan had “negotiated better.” She asked to see the salary band. HR declined.
What Keisha did not yet know was that “he negotiated better” is not a defense under the Illinois Equal Pay Act when there is no legitimate, bona fide factor justifying the pay gap. Salary history — which Illinois law prohibits employers from asking about — cannot be used to perpetuate a wage disparity. Her employer had both an Equal Pay Act problem and a salary history inquiry problem.
Keisha called an attorney. Her case settled. She got the $11,000 difference per year times the period of underpayment, plus interest and fees.
The Details
The Illinois Equal Pay Act (820 ILCS 112/) was significantly strengthened in 2021 and again in subsequent amendments, creating one of the most robust state-level pay equity regimes in the country.
The core prohibition: Illinois employers may not pay an employee of one sex or race less than an employee of a different sex or race for substantially similar work. “Substantially similar” is measured by skill, effort, and responsibility performed under similar working conditions. The jobs do not need to have the same title — what matters is what the work actually requires.
Legitimate defenses: An employer can justify a pay differential if it is based on one or more bona fide factors that are not based on sex or race, including: (1) a seniority system; (2) a merit system; (3) a system measuring earnings by quantity or quality of production; or (4) a differential based on a factor other than sex or race. But the factor must actually explain the differential — not simply be asserted as a justification.
The salary history prohibition: Under 820 ILCS 112/10.5, Illinois employers cannot screen job applicants based on their salary history or ask about prior compensation. This was enacted specifically to prevent the perpetuation of historical pay gaps — a woman who was underpaid in a prior job cannot be offered a lower salary at a new job based on that history.
The Equal Pay Registration Certificate (EPRC): This is where Illinois gets truly distinctive. Under the 2021 amendments, private employers with 100 or more employees in Illinois must register with the IDOL and obtain an Equal Pay Registration Certificate. To do so, they must submit a copy of their federal EEO-1 report, a list of all employees by county of employment and by classification, and a signed compliance statement certifying pay equity. The EPRC must be renewed every two years. Failure to obtain or renew the EPRC carries a civil penalty of up to $10,000.
Private right of action: An employee who believes she has been paid unequally in violation of the Act can file a complaint with the IDOL or bring a private lawsuit. Remedies include: the wage differential (the difference between what the employee was paid and what a comparable employee of a different sex or race was paid), interest on unpaid wages, and attorney’s fees and costs. There is a three-year statute of limitations under the Illinois EPA, and the limitations period restarts with each discriminatory paycheck.
The federal connection: The federal Equal Pay Act (29 U.S.C. § 206(d)) and Title VII of the Civil Rights Act also prohibit pay discrimination. Illinois workers can pursue claims under both state and federal law simultaneously, potentially accessing broader remedies. The Lilly Ledbetter Fair Pay Act ensures the federal statute of limitations resets with each discriminatory paycheck as well.
The Toolkit
| Concept | What It Means | Why It Matters to You |
|---|---|---|
| Substantially Similar Work | Compared by skill, effort, responsibility, and working conditions — not job titles | A female VP can be compared to a male VP even in different departments if the work is comparable |
| No Salary History Inquiries | Illinois employers cannot ask about or use prior salary to set compensation | Your past underpayment cannot follow you to a new job under Illinois law |
| Equal Pay Registration Certificate | Required for 100+ employee Illinois employers every two years | Employers must certify pay equity — creating a paper trail for IDOL audits and litigation |
| $10,000 Penalty | Per violation for failure to obtain or renew the EPRC | Creates strong incentive for large employers to audit their pay practices proactively |
| 3-Year Statute of Limitations | Resets with each discriminatory paycheck under Illinois law | A long-running pay disparity may allow recovery going back years from the date of filing |
The Algorithmic Shadow
Pay equity is increasingly determined by algorithm. Compensation platforms used by large Illinois employers set salary ranges, generate offer recommendations, and calculate merit increases — all through automated systems trained on historical pay data. If that historical data contains decades of pay disparity between men and women, or between white employees and employees of color, the algorithm learns and replicates those patterns. The result is algorithmic pay discrimination at scale, affecting thousands of workers across Cook County and DuPage County simultaneously, with no single human decision-maker to blame.
The Equal Pay Registration Certificate requirement is a direct legislative response to this problem. By requiring employers to disclose and certify their pay data, Illinois creates a mechanism for IDOL to identify patterns that no individual employee could detect on their own. Ahmad Sulaiman believes the EPRC data, combined with discovery in private litigation, will become one of the most powerful tools for exposing algorithmic pay discrimination in the next decade. If you suspect you are being paid less than a comparable colleague of a different sex or race, the law now requires your employer to have records that could prove it.
Frequently Asked Questions
Does the Illinois Equal Pay Act apply to me if I work for a small employer?
Yes. The core prohibition against unequal pay for substantially similar work applies to all Illinois employers regardless of size. The EPRC registration requirement is limited to employers with 100 or more employees, but the right to equal pay extends to every worker in Illinois.
My employer says I earn less because I did not negotiate as hard. Is that a valid defense?
Not if your prior salary — which was also lower — is what set the baseline for negotiation. Illinois’s salary history prohibition was enacted specifically to prevent this circular reasoning. If you can show the wage differential tracks a protected characteristic and is not explained by legitimate factors like seniority or merit, the employer’s negotiation defense may fail.
Can a man use the Illinois Equal Pay Act?
Yes. The 2021 amendments extended the Act’s coverage to race-based pay disparities and maintained its application to any sex-based disparity. A man paid less than a woman for substantially similar work has the same rights. The Act protects against pay discrimination based on sex — in either direction.
How do I find out if I am being paid less than coworkers in Illinois?
Illinois does not currently require employers to disclose individual employee salaries. However, the EPRC data is partially public. You can also gather information through colleague conversations (which are protected under the NLRA), salary surveys, and discovery in litigation. Illinois law prohibits employers from retaliating against employees for discussing their wages with coworkers.
What is the process for filing an Illinois Equal Pay Act complaint?
You can file a complaint with the Illinois Department of Labor at labor.illinois.gov, or bring a private lawsuit in Illinois circuit court. The three-year statute of limitations gives you time to gather evidence before filing. An attorney can help you assess the strength of your case and determine whether a private lawsuit or IDOL complaint is the better path.
Can I be fired for asking about pay equity at my Illinois workplace?
No. The Illinois Equal Pay Act explicitly prohibits retaliation against employees who inquire about, discuss, or disclose their wages or the wages of another employee. An employer who fires or disciplines you for asking pay equity questions has committed a separate violation subject to additional remedies.
Ahmad Sulaiman and Atlas Law Center represent Illinois workers who suspect they are being paid less than what the law requires. Pay discrimination is one of the most pervasive and underreported violations in the workplace — often hidden in plain sight behind closed-door salary decisions. If something feels wrong, it is worth a conversation.
Contact Atlas Law Center for a free consultation — Employment Law: (630) 394-6350 | Consumer Law: (331) 321-4748. Care first. Justice always.