Can employees request to change their scheduled day off?

Question Details: We own a chain of businesses, that typically employ 1 person per day per location. We have 22 locations, and each is open 6 days a week. Employees only work 5 days a week. We then have floaters which work 5 days a week, at 5 different locations, covering the store managers' days off. Therefore, 1 manager may typically be off on a Monday and another on a Tuesday, and so on, in order for floaters to get a regular schedule. If an employee is typically off on Wednesdays and they have a doctor's appointment in 3 weeks on a Thursday, and the schedule has not been put out for that week, can the employee request to change their next scheduled day off to be Thursday as opposed to the normal Wednesday, in order to not have to use a vacation day for that? I am VP of the company,and want to make a rule going forward. We have typically done this in the past, however our HR manager just sent a mass email for the new year saying employees can no longer change their next day off to work around their schedule. Our stance has always been to work with employees and we would like to keep it that way. Are there any laws pertaining to this?

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