The Memorial Day weekend typically marks the start of the summer vacation season, which for about three-fourths of American workers will mean the possibility of some paid time off.

The United States is the only highly developed nation that doesn't require employers to offer paid vacation time, according to a new report from the Center for Economic and Policy Research, a left-leaning think tank.

The report examined vacation policies in 21 developed countries, including the United States. The researchers found that every country except the U.S. had laws making employers offer between 10 and 30 paid vacation days a year.

(Read More: How Much Americans Think They Need to Get By)

France's laws granted employees the most paid vacation—30 days a year. But several countries actually guarantee workers more total paid time off when mandated paid holidays are added.

Japan and Canada were at the lower end of the list, with laws that require employers to offer 10 paid vacation days.

The researchers found that 77 percent of U.S. workers get paid vacation time. The workers who do receive it get an average of 13 days a year, according to the analysis.

Full-time U.S. workers were much more likely than part-timers to get paid vacation, and higher- wage workers also were considerably more likely than lower-wage ones to have that benefit, according to the report.