This Date in History: January 29, 2009

Four years ago today, a newly elected President Barack Obama delivered on a campaign promise and signed into law the Lilly Ledbetter Fair Pay Act. The law makes it easier for women to effectively challenge unequal pay.

Ms Ledbetter, who discovered her employer was paying her less than men for the same work, took her pay discrimination complaint all the way to the Supreme Court. The court ruled in 2007 that claims like hers had to be filed within 180 days of an employer’s decision to pay a worker less—even if the worker didn’t learn about the unfair pay until much later, as was the case for Ms Ledbetter.

To make sure that people can effectively challenge unequal pay, the law President Obama signed shortly after taking office amended the Civil Rights Act of 1964 so that unfair pay complaints can be filed within 180 days of a discriminatory paycheck—and that 180 days resets after each paycheck is issued.