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(CNN) -- In public and behind closed doors, 2016 Republican presidential candidates are being put on the spot on an increasingly tricky issue: same-sex marriage.

The issue has become a source of friction within the Republican Party, as more socially liberal donors and corporations clash with conservative activists and other opponents of same-sex marriage. Marco Rubio was the latest GOP candidate to field this question at a private fundraiser with party elites in Washington on Wednesday night.

One donor identified himself as gay and asked the Florida senator to state his position on same-sex marriage during a question-and-answer session, two attendees who were in the room told CNN.

Rubio stuck to his conservative position: He said he personally believes marriage should be between a man and a woman, though he said individual states can choose their own policies related to same-sex marriage.

Rubio spokesman Alex Conant declined to comment.

‪The interaction highlights the complicated balancing act Republican presidential candidates now face, as they must defend their social views to political donors while avoiding inconsistency in their public statements.‬

Republican officials have struggled to adapt to the country's changing views on same-sex marriage. Just this year, contentious debates over the so-called "religious freedom" laws in several states also exposed a growing rift between socially conservative Republicans and big business, which has historically backed the GOP.‬

Some of Rubio's fellow presidential aspirants have run into some trouble on the issue.

Texas Sen. Ted Cruz, an outspoken opponent of same-sex marriage, was forced to reaffirm his position last month after it was reported that the presidential candidate seemed to have softened his view in a private gathering of donors. (Cruz had told supporters that he would love his daughters just the same if he learned that any one of them was gay, The New York Times first reported.)

Former Florida Gov. Jeb Bush has also been scrutinized for his statements on same-sex marriage. In one recent interview, Bush, who has not yet officially launched his presidential campaign, stood by his opposition to same-sex marriage, stating that he doesn't consider it a constitutional right.

If GOP candidates are feeling pressure from Christian conservatives to demonstrate their unequivocal opposition to same-sex marriage, some donors have landed in hot water for the opposite reason.

A gay businessman who hosted the New York City fundraiser for Cruz faced fierce backlash from the gay community and ultimately issued an apology for holding the event for the Texas senator, calling it a "terrible mistake."

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