Sen. Charles Grassley, R-Iowa, the top Republican on the Senate Judiciary panel with jurisdiction over the legislation, said he and party colleagues find the same-sex provisions "superfluous" because a 2005 reauthorization of the law included language prohibiting discrimination on the basis of religion, age and other criteria without specifying sexual orientation.
"The original legislation doesn't allow discrimination of any kind anyway," Grassley said in an interview.
Obama's immigration proposal calls for foreign nationals in same-sex relationships to be treated the same as other couples when petitioning for spousal visas. Immigration coverage for gay couples wasn't included in principles for a comprehensive overhaul released last month by a bipartisan group of senators.
Republican Sens. John McCain of Arizona and Lindsey Graham of South Carolina, who are among a bipartisan group of eight senators pushing for an immigration bill, have said that including same-sex marriage in the package would threaten a deal.
Rep. Jerrold Nadler, a New York Democrat who backs visas for gay partners, said in an interview that "keeping a loving couple apart" is "gratuitously cruel."
There were an estimated 28,500 same-sex couples with one non-citizen partner in the U.S. in 2010, according to a 2011 study by the Williams Institute, a group at the University of California-Los Angeles that focuses on lesbian, gay, bisexual and transgender research.