The best thing we can give dads this Father's Day is support for paid family leave.

"Take Time to Be a Dad Today!" exhorts a nationwide public service announcement promoting fathers' involvement with their children. But if the U.S. government really wants to promote fathers' involvement, it should adopt a proven policy: paid family leave.

Around the world, countries have for decades (in some cases for more than a century) had laws that guarantee paid, job-protected leave from work to care for new children or seriously ill family members.

A new book called "Children's Chances," published by Harvard University Press, shows that 180 countries now guarantee paid maternity leave under law, and at least 81 guarantee paid leave for fathers upon birth or adoption of a child. The United States is not one of those countries.

The federal Family and Medical Leave Act (known as the FMLA) enables workers with new children or family members with serious medical conditions to take unpaid leave, but about 40 percent of the work force is not covered. Many workers who are eligible for FMLA leave cannot afford to take unpaid leave. There is no national law on paid parental or family leave.

Only California and New Jersey have paid family leave insurance programs, offering up to six weeks of partially paid family leave, entirely funded by small worker payroll contributions.

A few states offer temporary disability payments to mothers after childbirth.

In all other states, paid family leave is up to the whim of employers.

According to the Bureau of Labor Statistics, only about 12 percent of the work force has paid family leave benefits. High-income workers are far more likely to have paid family leave than low-income workers. Some workers can scrape together vacation or sick pay when a child is born, but many workers (especially those who are low income) have no paid sick leave.

Opponents of paid family leave assert that it would be too hard on businesses or the economy in today's tough financial climate. But economists, social scientists and other experts have studied various forms of paid family leave for decades and have found positive impacts on productivity, staff turnover, public health and economic competitiveness, even when times are tough.

The California and New Jersey programs have also shown good results. A 2011 survey of the California family leave insurance program reflected the views of 253 employers and 500 employees. The vast majority of employers reported that paid family leave had a positive or no noticeable effect on productivity (89 percent), profitability (91 percent), turnover (96 percent) and employee morale (99 percent). Thanks to the program, many more men could indeed "take time to be a dad."

On Father's Day, we'll no doubt hear more calls for dads to spend time with their kids. Now it's time for a national policy on paid family leave to make this feasible.

Janet Walsh is deputy women's rights director at Human Rights Watch and the author of "Failing its Families: Lack of Paid Leave and Work-Family Supports in the US." Follow her on Twitter: @JanetHRW She can be reached at pmproj@progressive.org.