NEW YORK (CNN/Money) - Women received less salary than their male counterparts partly because they generally work fewer hours than men, are likely to leave the labor force for longer periods and tend to hold jobs that pay less, a congressional study found.

But even after accounting for key factors that affect earnings, women, on average, make only 80 percent of what men earned in 2000, according to the study released on Thursday by Democratic Reps. Carolyn Maloney of New York and John Dingell of Michigan.

"This startling new data shows that in seven of the ten industries studied, the wage gap between male and female managers widened between 1995 and 2000," Dingell said in a statement. "It's compelling evidence that the glass ceiling remains a powerful obstacle to women in the workforce, and it suggests things may be getting worse, not better."

The 20.3-percent gap has been relatively unchanged in the past 20 years, while the smallest gap occured in 1983 with 19.6 percent.

YOUR E-MAIL ALERTS Follow the news that matters to you. Create your own alert to be notified on topics you're interested in. Or, visit Popular Alerts for suggestions. Manage alerts | What is this?

The Dingell-Maloney study said it couldn't explain all of the differences in earnings between men and women but noted that experts have speculated the earnings difference may result from discrimination in the workplace or subtler discrimination about what types of career or job choices women can take.