Pennsylvania Senator Bob Casey on Monday dropped his opposition to gay marriage.

“After much deliberation and after reviewing the legal, public policy and civil-rights questions presented, I support marriage equality for same-sex couples and believe that DOMA should be repealed,” Casey said in a statement given to gay weekly Philadelphia Gay News.

“If two people of the same sex fall in love and want to marry, why would our government stand in the way? At a time when many Americans lament a lack of commitment in our society between married men and women, why would we want less commitment and fewer strong marriages? If two people of the same sex want to raise children, why would our government prevent them from doing so, especially when so many children have only one parent or none at all?”

“As a senator and as a citizen, I can no longer in good conscience take a position that denies [gay couples] the full measure of equality and respect.”

Following the endorsements of six Democratic senators, activists mounted a campaign calling on Casey, who previously backed civil unions, to join his colleagues on the issue.

More than 12,000 people signed on to an online petition started by Michael Morrill, executive director of Keystone Progress.

Additional pressure came from Pennsylvania State Rep. Brian Sims, who wrote an open letter to the senator.

“We have believed since you were sworn in that when the time was right, when it really mattered, you would be there for equality,” wrote Sims, who is openly gay. “The time is right and we need you to be here.”

“But your voice is silent. And I am angry.”

“Please, senator, don't wait any longer to take a stand. Show and voice your support for full equality for LGBT Americas today,” he concluded.

Casey joins a growing list of U.S. senators who have recently reversed course on the issue, including Senator Rob Portman, a Republican from Ohio, and Democratic Senators Claire McCaskill of Missouri, Mark Warner of Virginia, Mark Begich of Alaska, Jon Tester of Montana, Jay Rockefeller of West Virginia and Kay Hagan of North Carolina.