On average, women make about 20 percent less than men.
Tuesday’s date marks the extra four months and four days women have to work to match the salaries their male counterparts made last year.
Companies including Lyft and Procter & Gamble are offering 20 percent discounts on their products to mark the day.
Congress is also planning to reintroduce a bill that would strengthen protections for women in the workplace.
Hundreds of businesses in 25 cities are taking part in the campaign.
For more information about Equal Pay Day, click here.