The letter is addressed to Cardinal Timothy Dolan, president of the United States Conference of Catholic Bishops.
Dolan says he has insights he's sharing with fellow bishops.
Dolan said the movement against marriage equality is 'not antigay,' but 'aimed at opposing a range of threats.'
He sent a letter to President Barack Obama.
“This isn't a question of civil rights,” he said.
He took to his website to compare the legislation to living under Communist regimes like China and North Korea.
The comparison was made during a national 60 Minutes interview.