The treaty's defenders say it will would help protect the rights of American and other nations' disabled citizens, who in some parts of the world face discrimination and mistreatment.
The treaty's detractors say the language is overly broad, and the Republican platform adopted at the party's national convention opposed it.
"There are some very, very troubling provisions that could open up Pandora's Box that could directly affect many families in America, particularly with children who have disabilities," Santorum said, with his youngest daughter Bella, who suffers from a rare genetic disorder, starting to cry at his side.
President Barack Obama signed the treaty in 2009 but sent it only this May to the Senate where it's been held up by conservatives worried that it would hand over too much power to the United Nations. The fears extend to hypothetical scenarios in which the international group would decide how many disabled parking stalls are reserved at churches, enshrine abortion and gay rights and force homeowners to install wheelchair ramps.
Sen. Orrin Hatch, R-Utah, also says he has concerns with the treaty and joined 35 other senators in a letter opposing any ratification during the lame-duck session.
"Senator Hatch supports the treaty's general goal of advancing the rights and opportunities of persons with disabilities," said Hatch spokesman Matt Harakal, "but he does not support the means that the treaty uses to achieve that goal out of concern that the treaty could jeopardize American sovereignty."
The Senate Foreign Relations Committee in July agreed to join the convention on a 13-6 vote, with three Republicans agreeing to the treaty and six, including Lee, opposed.
Senate Foreign Relations Committee Chairman John Kerry said in a July hearing on the treaty that it would extend protections and liberties to Americans when traveling abroad as well as to disabled members of the military. There's no downside to ratifying it, Kerry said.
"The United States is already a leader in domestic disability rights protection," Kerry said. "Joining the convention will provide a critical tool as we work with other countries to advocate what they follow and hopefully that they will follow our lead and ensure that people with disabilities are free to live and work and travel wherever they want."
Kerry also noted that in the developing world, people with disabilities face indignities and prejudices on a daily basis and backing the treaty would strengthen the United States' cause in pushing for higher standards.
United Nations disabilities treaty
To read the U.N.'s Convention on the Rights of Persons with Disabilities, go to http://www.un.org/disabilities/convention/conventionfull.shtml.