Md. Code, Business Regulation § 15–204

(a) An innkeeper may require a prospective guest to demonstrate an ability to pay by cash or valid credit card.

(b) An innkeeper may require each guest at a lodging establishment to register and may require the guest to produce:

(1) a valid driver’s license;

(2) a valid uniformed services identification card;

(3) a valid passport; or

(4) any valid government issued identification card.

(c) An innkeeper may limit the number of individuals who may occupy a particular guest room in a lodging establishment.