We're now entering the most popular months of the year for vacation, but not all full-time workers have that opportunity if they still want to get paid. In fact, according to a new report, the United States is the only "rich" country that doesn't require paid vacation time.

The report from the Center for Economic and Policy Research examined 21 developed countries for their vacation policies. Every country besides the United States guaranteed workers between 10 and 30 vacation days per year.

"Americans work longer and harder than anybody else in the world, and we don't always benefit from it," said Lewis Maltby, President of the National Workrights Institute in Princeton. "Everybody needs a little time off."

When employees don't receive paid vacation time, according to Maltby, everyone loses. He said it's the time off that makes an employee more productive for the rest of the year.

Despite no requirement in the U.S., more than three-quarters of workers receive paid vacation time, at an average of 13 days.

"People are not machines," Maltby added.

The struggling economy has presented another troubling trend; those with paid vacation time may be afraid to use it. They don't want to risk their jobs and show a lack of motivation, especially if other workers on an equal level are skipping the same benefit.