Facebook (FB) COO Sheryl Sandberg is taking her fight for equal pay for women to the next level. This Equal Pay Day, Sandberg has proposed that companies be transparent about their pay scales and other performance metrics for men and women.

“I think it's really important for companies to be very transparent in how they pay people. It's also really important to be very transparent and audit yourself on whether or not you are paying fairly,” she said in an interview with NPR’s Marketplace this morning, “We're looking at our performance ratings. We're looking at our pay rates, and we're looking at our promotions to make sure that women and men are being treated fairly. More companies need to do this.”

Pay Gap

The latest figures reveal a 20% difference in pay for men and women for similar work. The U.S. Census Bureau’s 2015 Income and Poverty data shows that median earnings for women with full time employment that year were $40,742. For every dollar that a man earned on average, a woman made 81 cents.

Sandberg’s non-profit Lean In, which works in the area of gender equality, has teamed up with retailers to give discounts this Equal Pay Day. P&G (PG) is offering a rebate on certain purchases between April 2 and April 30; Lyft is donating 20% of what it will make on rides (max. $100,000) on April 4 to organizations working for women and children; and Luna Bar is offering 20% discount on its bars April 3 - 11 and matching the amount with a donation (max.$100,000).

“There are hundreds of businesses in 25 U.S. cities offering 20 percent discounts on everything from coffee to pizza and pet supplies,” Sandberg told Marketplace.

Participation

Four years after she wrote "Lean In: Women, Work, and the Will to Lead," Sandberg feels that women are still not better off in terms of workplace equality. In an interview with USA Today, last month Sandberg said, “We are not seeing a major increase in female leadership in any industry or in any government in the world, and I think that's a shame.”

According to non-profit Catalyst.org, only 29 or 5.8% companies in the S&P 500 have women CEOs. Data from Center for American Women and Politics, Rutgers University shows that women make up 19.4% for the U.S. Congress and 24.9% of the State Legislature.