First, you are by no means required to offer an alternate day off of work. However, most employers do elect to offer another day off when a holiday falls on a weekend. The most common policy we see is that if the holiday falls on a Saturday, the Friday before is given off. And if the holiday falls on a Sunday, the Monday after is given off. Consequently, we anticipate that most office employers will be closed on Monday, December 26th and Monday, January 2nd.
If you are concerned about shift or client coverage on those Mondays, a less common but more creative approach is to implement flex holidays. With this option, you would allow half of your workforce to have the Friday before the holiday off and the other half to have the Monday after the holiday off. You could even allow them to select which one they would prefer. This option is often a nice way to handle holidays for companies that are concerned about shift coverage and would like at least a skeleton crew to manage pressing issues. Everyone gets a three-day holiday weekend, but with the least amount of disturbance to clients. And employees often appreciate the flexibility of selecting their day off around the holidays.