Broken foot? Ate some bad leftover turkey? Caught the flu? Want a day off?

For many, taking a sick day requires little thought. But by most estimates, nearly half of all private-sector workers in the United States do not have a single day of paid sick leave. And more do not have a paid day off that can be used to care for a sick child.

Low-wage workers are hit the hardest, with three of every four lacking any paid sick leave. They also usually have no health-care coverage and work a full-time or more than full-time schedule of piecemeal, part-time jobs, making paid sick leave even more unlikely.

When workers without sick leave get a virus or an injury, they have to decide if they can take an unpaid day off and still make the rent. If not, they often return to their jobs as security guards, cooks, waitresses and cashiers -- decreasing their productivity and possibly getting others sick. Paid sick days can reduce turnover, cut down on health-care costs (although most companies that don't provide paid sick leave also don't provide health-care coverage), and increase productivity and morale.

There was movement on the paid-sick-day front last month. More than 60 percent of voters in San Francisco approved a ballot measure that would require all businesses with fewer than 10 workers to give employees up to 40 hours of paid sick leave a year; for larger employers, up to 72 hours. At every company, an employee will accrue one hour of paid sick leave for every 30 hours worked, so both part-time and full-time workers would be covered.

It probably won't end with San Francisco. There is a push to get similar measures in front of decision-makers in other cities and states in the coming year.

"I think it really helps add momentum," Debra Ness, president of the National Partnership for Women & Families, said of the San Francisco initiative.

The partnership and other groups are behind the efforts to require employers to provide paid sick time. Although the federal Family and Medical Leave Act requires every employer of 50 or more to provide up to 12 weeks of unpaid sick leave, many people can't afford to take that time off.

A 2004 Harvard University study reported that 139 countries provide paid leave for short- or long-term illnesses. And 117 of those nations guarantee workers a week or more of paid sick days per year.

At least 37 countries have policies guaranteeing parents some type of paid leave when their children are ill. The United States does not.

Randel Johnson, vice president of labor with the U.S. Chamber of Commerce, pointed out that Europeans' sick leave is usually subsidized by their governments, not the businesses themselves. "Money doesn't grow on trees," he said.

Organizations working for paid sick leave have been battling with groups that say making it mandatory would be a burden on businesses -- especially small businesses. But companies in San Francisco are not yet putting up a fight against the measure, which is to become law Feb. 5.

There is movement among federal lawmakers as well.

Sen. Edward M. Kennedy, D-Mass., and Rep. Rosa L. DeLauro, D-Conn., introduced the Healthy Families Act in 2005, to require that employers with at least 15 employees provide seven days of paid sick leave annually for full-time employees. Part-time employees would get prorated leave depending on the hours they worked. The leave could be used for the medical needs of employees or their family members.

The bill will be reintroduced in the next session, and Mr. Kennedy's office expects that the Democratic majority will help it go further. Hearings are expected in the first few months of next year.

According to a recent survey, 65 percent of New York City's working poor -- the 340,000 people who work and live in households below the federal poverty level of $16,000 for a family of three -- have no paid sick days.

"People with families who are living paycheck to paycheck don't have the savings to make up for a lost day's pay," said Nancy Rankin, director of research at the Community Service Society of New York.

Of low-income workers without paid sick days, 31 percent said they did not have even $100 in savings to fall back on, the survey showed.