Sheryl Sandberg's new mission on Equal Pay Day: #20PercentCounts

Corrections & Clarifications: The 20% discount will be available to men as well as women. 

SAN FRANCISCO — Lean In's Sheryl Sandberg is calling attention to the gender pay gap with a national retail campaign that will offer discounts to women on Equal Pay Day.

The reasoning behind the #20PercentCounts campaign that launches Tuesday: If a woman makes 20% less than a man, she should pay 20% less for the purchases she makes.

Three hundred local businesses in 25 cities will offer 20% discounts or special offers to women and men, too.

Equal Pay Day is a symbolic point in the year that represents the date that working women's pay catches up to men's from the prior year.

Women on average are paid 20% less than men in the U.S., black women 37% less and Hispanic women 46% less, says Sandberg. For women of color, Equal Pay Day comes much later in the year. Black women have to work until July 31 and Hispanic women until November 2 to catch up.

Little progress has been made in narrowing the gap since President John F. Kennedy signed the Equal Pay Act more than a half century ago, says Sandberg, founder of LeanIn.org and chief operating officer of Facebook.

"Pennies," she told USA TODAY in an interview. "Pennies."

The #20PercentCounts campaign was spearheaded by Lean In circles, the peer support groups that sprang from Sandberg's 2013 bestseller Lean In: Women, Work, and the Will to Lead. This is the fourth year of the campaign for Lean In DC, which came up with the idea, and the first year it has gone national, says Hilary Badger, who sits on Lean In DC's executive board.

Panbury's Pie Cafe in Atlanta, Georgia, Builders' Hardware in East Lansing, Mich., Found Coffee in Los Angeles and Wiley's Comedy Joint in Dayton, Ohio, are among the local businesses offering 20% discounts.

National partners for the Lean In campaign are LUNA, Lyft, Procter & Gamble and Salesforce. LUNA is offering 20% off of bars sold on its website from April 3 to April 11. Lyft is donating 20% of ride fares on Tuesday to organizations that help women and families. Procter & Gamble is offering a rebate on some products. Salesforce donated in-store signage, online advertising and local events, according to Lean In.

"To see businesses take a stand, this is how we value women's labor, is really exciting," says Badger.

According to Lean In, shortchanging women's paychecks unfairly penalizes women and their families, reducing how much they can spend on groceries to how much they can put away for their children's education.

If the pay gap were erased, the average woman would make $530,000 more over the course of her career, and millions of women and families would be lifted out of poverty, Lean In says. Practically speaking, that means women on average could afford 78 more weeks of groceries each year. Black and Hispanic women could afford 155 additional weeks and 193 additional weeks of groceries, respectively.

"We have to understand that the pay gap is happening to women and men with similar jobs that require similar skills and similar educational levels — and that has a real impact," Sandberg said. "The number of working women living in poverty would be cut in half if women were just paid the same as men. So this is important for our businesses and this is important for our country."

Few people dispute there's a wage gap, but not everyone believes it's as wide as Sandberg does. The Census Bureau says women earn 79 cents for every dollar that men earn, based on the median salaries of full-time workers. When it comes to weekly and hourly wages, the gap isn't as great, according to the Labor Department’s Bureau of Labor Statistics.

Some differences between women's and men's paychecks can be explained by factors including the average woman has less work experience than the average man, women take time off to raise children and they choose careers that tend to have more flexible hours and lower earning potential. But part of the gender pay gap can't be accounted for and stubbornly pops up in a range of occupations and industries.

Related:

Sheryl Sandberg: Four years after 'Lean In' women are not better off

Sheryl Sandberg tells women: 'Lean in harder'

Sheryl Sandberg to corporate America: Lean in on family leave

The pay gap could vanish for all women — sometime in the 23rd century

Sandberg, who has spoken out frequently on the wage gap, says her company, Facebook, conducts frequent audits to make sure it pays women and men equally. Her hope: that publicity from the #20PercentCounts campaign will spur more action, maybe even legislation.

A number of states have enacted equal pay laws. California, home base to Facebook, has one of the nation's toughest, requiring companies to prove they pay women and men equally for similar jobs. But proposed federal legislation, known as the the Paycheck Fairness Act, has repeatedly stalled in Congress.

Shareholders are getting more aggressive in pressuring companies, including Facebook, on equal pay. Still, surveys show the gender pay gap is a big problem in the technology industry.

"We need to raise the federal minimum wage law. Two-thirds of minimum-wage workers are women. We need better public policy. We need businesses to do the audits they should be doing. We need individuals to be aware of this," Sandberg said. "There is a lot to do."

Visitors to LeanIn.org's website will find data on the pay gap in the U.S. and globally as well as steps that companies can take to make sure they pay women fairly. A campaign video from Funny or Die and Hulu posted there imagines a woman's day with 20% less of everything, from coffee to smartphone batteries.