It's unclear who the senator is or what the precise objections are.
Two separate amendments -- from Sens. Edward Kennedy, D-Mass., and John Kerry, D-Mass. -- would require the national intelligence director to provide classified information on secret CIA prisons to congressional intelligence committees. The agency has not acknowledged that the sites exist.
The intelligence bill -- much of which is classified, "broadly sets spending for the more than $40 billion U.S. spy agencies."
Congressional aides, who spoke on condition of anonymity while the legislation's status was in flux, said at least one unidentified Republican is objecting to some portion of the bill, which could otherwise be passed unanimously by voice vote. That process would allow the Senate to quickly finish the legislation before the holidays and begin negotiating its differences with the House early next year.
Kerry's spokeswoman April Boyd noted the Senate already approved his secret prisons amendment on another bill this year.
"He would welcome another vote and another strong message from Congress to the administration that they cannot keep Congress in the dark," she said.
On Wednesday, Kennedy said he could find no reason why Congress shouldn't have the presidential briefings "now that the president's insisted that we had all the information."