This is a very interesting question that we unfortunately don’t have much coverage on.
There is no specific law that prohibits employers from mandating employees to share a hotel room during business travel, it is important to consider the potential negative impact on employee relations. Opting for such an arrangement may lead to issues in the long term, resulting in decreased employee morale, higher turnover rates, and reduced productivity. These consequences can ultimately outweigh any cost savings initially achieved.
Some of the cons of room-sharing may spill into other more regulated areas including employee privacy and even harassment.
Here are some related articles that may help you:
Can employers require employees to share a hotel room while on business travel to reduce costs? SHRM is US based but the information in this article would be applicable anywhere
Should Employees Share Their Rooms When Traveling for Business?
Why your employees shouldn’t be expected to share hotel rooms
Hope this helps!