Vacation trends are changing and the new direction may come as a shock.

American workers have traditionally taken approximately 20 days of vacation per year but that is down to an average of 17 days, Thrive Global reports.

And it turns out millennials are the worst offenders. This group is the least likely to take days off, but they are also typically entitled to the fewest number of vacation days.

Millennials are at least twice as likely to forfeit vacation time because they are too afraid of losing their jobs, according to the report.

This is in large part because many millennials entered the workforce during the economic downturn, which means once they landed a job, they had a strong desire to prove their worth. Many of them are also coping with crushing student loan debt, which has proved to compound the problem, Project: Time Off reports.

But millennials now make up about half of the workforce, which means this trend could have serious implications for future generations.