Bob Dole suggested Wednesday that fellow Republican Rob Portman doesn’t support ratifying the Convention on the Rights of Persons with Disabilities because the senator came out in favor of gay marriage.

That was the implication from a conversation between Dole and a veteran after an event promoting Senate approval of the treaty, which has been mired in controversy after conservatives said the treaty could diminish U.S. sovereignty and keep parents from home-schooling their children.

Surrounded by a scrum of reporters and well-wishers, Dole told a vet that one senator told him that he couldn’t support the treaty, negotiated by George W. Bush’s administration, because he had already “voted for same-sex marriage.”

Dole went on to say that he couldn’t see the connection between the two and pointed out that the senator in question had a gay son. This description can only match Portman, the Ohio Republican who opposed the treaty’s ratification when it first came up for a vote in 2012. Portman verbally endorsed same-sex marriage after his son came out as gay in 2013.

Portman’s office pushed back against Dole’s statement. Caitlin Conant, a Portman spokesperson, told The Daily Beast that Portman “didn’t say this and voted against the U.N. Convention on the Rights of Persons with Disabilities in the last Congress. His opposition has been focused solely on underlying policy concerns.” A spokesman for Dole said the former Senate majority leader and presidential nominee was unavailable for comment.

In addition to his vote against it, Portman was one of 36 GOP senators to sign a 2012 letter opposing the ratification of the treaty. However, at the time, according to WKSU Radio in Ohio, he said he “would want to see some slight changes and then I would consider it…as would a number of my other Republican colleagues who signed the letter as I did based on the fact that we believe that the Congress that duly elected ought to be making these decisions and not slipping it into a lame-duck session.”

Dole’s comments show the growing tensions within the Republican caucus about the treaty. Although the treaty is backed by establishment Republicans like Dole, John McCain, and George H.W. Bush, it has become a cause célèbre among social conservatives. Home-schooling advocates are especially opposed, as they +claim the treaty would cede “our sovereignty, parental rights, and the rights of people with disabilities to unelected, unaccountable UN bureaucrats.” The Senate Foreign Relations Committee approved the treaty on Tuesday by a 12-6 vote with all Democrats and two Republicans, McCain and John Barrasso, voting in favor.

As a treaty, the Convention on the Rights of Persons with Disabilities requires the support of two-thirds of the Senate, or 67 votes. When it was last brought to a vote on the floor in 2012, only 61 senators supported it.