Can an employer force me to share a hotel room with a co-worker?

My employer wants me to travel out of town, stay overnight and share a room with another co-worker. I learned of their room sharing practice early in my employment and informed my boss that I didn't feel comfortable sharing a room and told him that I wouldn't do it. Now I'm three months into my employment and arrangements have been made for me to share a room with a co-worker. I was clear again with my employer and told him that I wouldn't do it. I've heard that some people who share my feelings have paid the additional money to have their own room. I don't feel this is fair either as it is business travel, not personal travel. I realize that PA is an at-will state but can my employer force me to share a room? Can they force me to pay the additional money to have my own room?