President Barack Obama marked the 50th anniversary of Equal Pay Act that was supposed to abolish wage disparity based on sex by saying the gains made by women haven’t completely closed the gap on wages.

As more women become the main earner in households, the disparity in wages compared with men is putting more pressure on middle-income families, Obama said at a White House ceremony marking the occasion.

“And as I said in my inaugural address this year, our journey to equality is not complete until our wives, our mothers, our daughters can earn a living equal to their efforts,” he said.

The law signed by President John F. Kennedy was aimed at assuring women of paychecks equal to those of men doing the same work. In 1963, women earned about 59 cents to every man’s dollar for the same job.

Comparing the median weekly full-time earnings in 2012, women earned 80.9 percent of men, according to the Institute for Women’s Policy Research, a Washington-based research group, citing figures from the U.S. Bureau of Labor Statistics.

On an annual basis, the earnings disparity was 77 percent in 2011, the last data available, the group said, citing BLS data.

U.S. Representative Rosa DeLauro, a Connecticut Democrat, has introduced the Paycheck Fairness Act 16 times in eight consecutive congresses. The bill’s designed to close loopholes in current law, including a requirement that employers prove that pay disparities stem from seniority, productivity, or merit and not sex.