WASHINGTON -- Twenty years after the Family and Medical Leave Act became law, 4 in 10 workers aren’t eligible to take temporary, unpaid leave to recover from serious illnesses or to care for new children or sick relatives.

Some who are covered under the law - about 5 percent - say they can’t afford to take the leave when they need it, according to a Labor Department study released this week.

Signed by President Bill Clinton in 1993, the Family and Medical Leave Act guarantees employees the right to take up to 12 weeks off from work each year to care for themselves or their relatives without fear of losing their jobs or health insurance. The law was updated in 2008 to allow military families to care for injured service members for up to 26 weeks.

The law doesn’t require employers to pay any wages during the leave. It also doesn’t cover workers at companies that have fewer than 50 employees, or anyone who works less than 24 hours per week. As a result, 40 percent of employees don’t qualify for job-protected leave, the Labor Department study found.

The nonprofit advocacy group that wrote the original Family and Medical Leave Act is drafting proposals to expand the law.

“It was always intended to be a first step and not the last,” said Vicki Shabo, the director of work and family programs for the nonprofit National Partnership for Women & Family in Washington.

One proposal would extend coverage to more workers. Another would create a paid family-leave insurance program. Funded through a small payroll tax – employer and employee each would pay two-tenths of 1 percent – the insurance program would provide two-thirds of an employee’s wages for up to 12 weeks of leave, Shabo said.

U.S. Rep. Rosa DeLauro, D-Conn., might introduce legislation for the insurance program later this year.

Over the past two decades, workers have used the Family and Medical Leave Act 100 million times, according to the Labor Department study. It found that 13 percent of qualified employees had taken leave in the past year, but most didn’t stay away from work for very long. Forty percent of workers who took leave were away for 10 days or fewer, and more than 70 percent returned to work within 40 days. Women caring for new children took longer leaves, averaging 58 days.

Thirty percent of employers say the cost of administering the law is rising, but few businesses - just 1 percent - reported “very negative” impacts on productivity, career advancement, morale, turnover and profitability, the study found.

“I think the survey confirms what we have long known, which is that for workers who are covered and employers who are obligated to provide leave under the act, the law’s working very well,” Shabo said. But a significant number of people aren’t covered, she said, and those who are covered but don’t receive paid leave must put themselves in financial jeopardy.

“They often have no choice but to go back to work before they’re ready,” Shabo said.

Some business groups oppose any expansion of the Family and Medical Leave Act, warning that it would create considerable burdens for companies.

“Any mandated leave _ that’s another tax on the employers,” said Elizabeth Milito, senior executive counsel for the National Federation of Independent Business’ Small Business Legal Center, a trade association based in Nashville, Tenn.