Washington (CNN) -- A prominent gay rights advocacy group says a key congressional Democrat will push for new rights for same-sex couples in the Senate's immigration reform bill -- a move which could undermine the legislation's bipartisan support.
According to a spokesman for Immigration Equality, Vermont Democratic Sen. Patrick Leahy intends to offer an amendment later this month allowing foreign-born individuals in committed same-sex relationships with Americans to apply for green cards.
Currently, such rights apply to only to foreign-born men or women in heterosexual marriages with U.S. citizens.
"That's our expectation," said Steve Ralls, a spokesman for the group, which promotes equality in immigration laws for gay, lesbian, bisexual and transgender individuals. "After the meetings we've had with Leahy and his staff, the message is pretty clear."
A spokeswoman for Leahy refused to confirm Ralls' assertion. The senator is an outspoken proponent of expanded rights for same-sex couples, and proposed similar legislation in the past.
Under the plan, according to Ralls, gays and lesbians requesting green cards for foreign-born partners would have to be married if their states currently recognize same-sex marriages.
If their states do not recognize same-sex marriage, they would have to meet a series of requirements proving major emotional and financial commitments.
The list of requirements could include jointly owned property, shared child custody, joint bank accounts, joint credit cards, proof of a commitment ceremony and photographs of shared vacations and holidays with extended family, among other things.
Leahy, head of the Senate Judiciary Committee, will likely propose the change at some point after his panel starts considering amendments on May 9, Ralls said.
If Leahy moves forward with the amendment, it could destroy hopes for any significant GOP backing of the sweeping legislation. Florida Sen. Marco Rubio, one of Republican architects of the 844-page bill, said Tuesday that adding such a provision would not be politically feasible in the ideologically polarized Congress.
The bill "was not intended to cover everybody in every situation," Rubio told conservative radio talk show host Hugh Hewitt. "This immigration bill is difficult enough as it is. ... If you inject something like this in the bill, it will die. The coalition behind it will fall apart."
Rubio, a potential presidential candidate and one of four Republicans in the Senate's so-called "Gang of Eight" that authored the bill, stressed that he would withdraw his own support.
"I hope we can avoid this," he said. "This is not the issue to engage this in, or you will threaten the entire product."
It is significantly easier for Leahy to add the amendment to the bill while it is being considered by his panel.
Democrats hold a 10-8 majority on the Judiciary Committee, and can approve changes on a strict majority basis. Controversial amendments taken up by the full Senate will almost certainly be required to garner a 60-vote supermajority.
Members of the Democratic caucus only control 55 seats in the 100-member chamber.
Backers of the bill have been hoping to win as many as 70 votes in the Senate, in order to give the bill major momentum heading into the more skeptical, GOP-controlled House.