Is it legal to forbid workers from scheduling appointments during work hours?

Q: “Can we tell employees that they are not allowed to schedule any outside appointments during work hours? I have an employee who is constantly scheduling appointments during work hours and having to leave work for hours at a time. In the last two weeks alone, this employee has missed a total of 27 hours due to appointments scheduled during work hours. If we cannot restrict employee appointments outside of work, can I require general documentation of appointments without requesting any protected personal information?" – Kate, New York