Tuesday marked Equal Pay Day, representing the extra 104 days it would take for the average full-time, year-round working woman in the United States to be paid as much as the average man was in the previous year.

“I’ve been at this a while, and I’m really getting frustrated, and I’m really getting volcanic,” said Sen. Barbara Mikulski (D-MD), the longest-serving woman in Congress, at a Tuesday press conference with advocates and Democratic congresswomen.

Mikulski said it’s long past time to pass her Paycheck Fairness Act, which would update the original Equal Pay Act of 1963 to make it easier for women to share information with their coworkers about salaries and harder for employers to legally justify paying women less for the same work, and to give women better legal remedies if they find out that they’re discriminated against.

Equal Pay Day dates back to 1996, and the wage gap remains high even though it’s been more than 50 years since President Lyndon Johnson signed the Equal Pay Act into law.

“Women are still fighting the same battles,” Mikulski said. “We are tired of being sidelined, red-lined, pink-slipped, harassed, and intimidated.”

Skeptics of the gender wage gap say it’s misleading to cite the statistic that women overall are paid 78 cents on the dollar compared to men. It doesn’t account, they say, for women’s choices—whether it’s working fewer and more flexible hours, or in industries or college majors that happen to pay less.

But advocates say that misses the point. It’s true that the 78 cents figure doesn’t account for different industries and education levels, for instance. But controlling for those factors still doesn’t erase the gap—women are paid 7 percent less than men a year out of college even controlling for just about every possible difference other than gender.

“The pay gap is not myth. It is math,” said Lisa Maatz, vice president of government relations at the American Association of University Women, at the press conference.

The wage gap varies greatly by occupation, geographic region, and race and ethnicity. For instance, women of color have it the hardest, especially if they’re mothers—Black mothers are paid 54 cents to the dollar, and Latina mothers are paid 49 cents.

But whatever the reason—whether it’s outright discrimination, reduced opportunities for women, or social biases that burden women with more family caregiving duties—women are paid less than men, which hurts families who depend on women’s income.

The 78-cent figure is “not an apples to apples comparison, and we’ve never claimed that it was,” Maatz said. “What it should be, though, is a red flag.”

Sen. Elizabeth Warren (D-MA) noted that according to the latest Census data, men are paid more than women in 264 out of 265 job categories.

“That is not an accident. That is discrimination,” Warren said.

Sen. Kirsten Gillibrand (D-NY) noted that unlike in the “Mad Men” era, 40 percent of women are their family’s primary or sole breadwinner.

Eight in ten moms are also working, and they suffer an even larger pay gap. Mothers are paid 71 cents to the dollar compared to fathers. For single mothers, that plummets to 58 cents.

It’s also true that public policy shapes women’s “choices.”

“We talk equal pay for equal work, but we also need to talk about the fact that jobs that are traditionally female are undervalued,” Maatz said. The top three jobs for women in 2015 are the same as they were in 1960: secretary, teacher, and nurse.

And even those low-paying, female-dominated fields have pay gaps. Ninety percent of nurses are women, but male nurses are still paid $5,100 more per year.

The Paycheck Fairness Act bans employers from retaliating against employees who discuss their wages. A Republican alternative introduced this week would do the same, but advocates say it wouldn’t close the loopholes that let employers discriminate in the first place, or that let employers write off pay discrimination as a “cost of doing business” because it’s cheaper to pay women less than to settle the occasional lawsuit.

AnnMarie Duchon, a member of Moms Rising, told her story of trying to recoup more than $12,000 of lost income after she found out that her male coworker—who had the same job and a nearly identical resume—was paid more.

Duchon finally got a raise, but it took seven years. And this was at a progressive public university that prided itself on diversity, she said.

“All of this occurred in an environment where I could have open conversations about my salary without fearing repercussions,” Duchon said. “Many employees are not so lucky.”

Todd Lamonia, a small business owner, spoke to that reality. He talked about the gender pay disparities he saw in the corporate IT world. There was no official policy barring discussions about wages, he said, but the culture strongly discouraged it.

He was building his career and didn’t feel empowered enough to speak out about the wage discrepancies, he said, but he knew he could at least subtly raise wages for his own team to make them fair.

“This shouldn’t have been an act of subterfuge,” Lamonia said.