"A private employer can fire you at any time for any reason as long as it is not an illegal reason," he said.
But he said it would not look good in the public's eye for Hopkins to discipline Carson.
"It would be really bad form for Hopkins to try to put controls on public debate over something like this," said Collins, a partner at Kahn, Smith & Collins.
Hopkins has not said it would discipline Carson. In his letter, Rothman acknowledged Carson has a right to his opinions.
"Dr. Carson has the right to participate in public debates and media interviews and express his personal opinions on political, social and religious issues," Rothman wrote. "We strongly value freedom of expression and affirm Dr. Carson's right, as a private citizen, to state his personal views."
The Rev. Jamal Bryant of Baltimore's Empowerment Temple said Carson shouldn't be faulted for his views simply because they are not popular with some in society. Bryant was among several African Methodist Episcopal Church leaders in Maryland who met this week and passed a resolution reaffirming their stance that marriage should be between a man and a woman.
"The wings of society at this point are moving in a supportive direction of same-sex marriage, and that it is a sensitive issue," Bryant said. "But I think he has the right as a private citizen to express that view."