Mitt Romney's opposition to gay marriage is at odds with several major donors to his campaign.

Romney's opposition to the institution played a key role in winning over social conservatives during the early days of the presidential primary.

Republican hedge fund managers Paul Singer, Dan Loeb and Cliff Asness backed the effort to legalize gay marriage in New York with six-figure checks. Singer, the head of Elliott Associates, has donated $8 million to the cause of marriage equality since 2007, according to the New York Times. He's also contributed $1 million to the super PAC supporting Romney and helped raise more than $1 million for his campaign.

The National Organization for Marriage (NOM), the nation's most vociferous opponent of gay marriage, endorsed Romney for president on Wednesday, the day after Rick Santorum suspended his campaign.

Gay rights groups quickly called on Romney to repudiate NOM's endorsement, noting the recent revelations that the group pursued a strategy to pit minority groups against gay marriage supporters.

One Republican insider told that donors are “often a reflection of where the public attitudes are.”

The issue is increasingly dividing the GOP.

For example, it was with the help of Republican lawmakers that the New Hampshire House recently rejected a Republican-sponsored measure which would have repealed the state's 2-year-old gay marriage law. And Republican lawmakers in New York played a key role in approving the state's gay marriage law last year.

R. Clarke Cooper, the executive director of gay GOP group Log Cabin Republicans, told that he urged Romney to tone down his rhetoric on the issue after he touted his role in keeping Massachusetts from becoming “the Las Vegas of gay marriages” during CPAC in February.

“I did say to him, your comments regarding marriage are not only not helpful but can be distracting from the campaign,” he said.

But pivoting or softening his stance on gay marriage would be a mistake, said conservative strategist Keith Appell, who represents NOM.

“Romney is well aware of the disastrous, long-lasting impact on the Republican Party that occurs when Republican presidents break pledges,” he said.