A bipartisan bill aimed at combating human sex trafficking has hit a major snag after Senate Democrats -- who unanimously voted to move the bill out of committee -- hit the brakes upon discovering a Republican-backed abortion provision.

Though the relatively modest 68-page bill has been available for nearly two months, it wasn't until this week that Senate Democrats said they noticed the language, and subsequently threatened to block the bill.

As drafted, the legislation would crack down on what lawmakers in both parties agree is a seamy underworld of drugs and human sex trafficking akin to modern-day slavery. Fines paid by those convicted of the sex-trafficking crimes would go into a fund to help victims.

But Democrats now are balking because the legislation also contains a Republican-inserted provision that bars the use of fines to pay for abortions, except in cases of rape, incest or when the life of the pregnant woman is in jeopardy.

"Democrats believe that divisive issues like this should be kept off what is otherwise a broadly bipartisan bill," a spokesman for Senate Democratic Leader Harry Reid said, adding that they're trying to find a "path forward." 

Republicans cast this as a routine extension of the so-called Hyde Amendment, which bans the use of federal funds for abortions except in limited circumstances. But Democrats said the legislation would mark a significant expansion since it applies to personal funds paid in fines. They also noted the restriction against the use of fine money would be permanent, while the one that applies to federal funds would lapse unless renewed on a year-by-year basis. 

Reid said in remarks on the Senate floor that "a number of people feel that it was by sleight-of-hand" that the provision was included in the measure, while "others say staff should have seen it was in the bill." A day earlier, others in his party had said flatly that no one on their side of the aisle had been informed. 

But Sen. John Cornyn, R-Texas, said Democrats had, in fact, known of the abortion-related provision that Republicans backed, citing discussion among aides of both parties. 

Republicans ripped Democrats for stalling over this issue. 

"This is really not an honorable time or a laudable time in the history of the United States Senate," said Sen. John McCain, R-Ariz. 

The events presented a difficult challenge for Democrats, forcing them to decide if their support for abortion rights justified blocking passage of a sex trafficking measure designed to help children and women. They privately conceded they lacked the votes to strip out the abortion portion of the bill they oppose, although they expressed confidence they had enough support to prevent passage of the entire measure. 

At the same time, they were forced to consider whether their aides had failed to read the bill closely enough to discover the provision when the bill was made public in January, or when it was approved unanimously in the Senate Judiciary Committee late last month. 

A statement released by a spokeswoman for the Democrats on the panel said Sen. Patrick Leahy, the party's senior committee member, did not know in advance that the abortion-related provision had been included, nor did his aides. 

A spokesman for Sen. Amy Klobuchar of Minnesota, the bill's leading Democratic supporter, said the lawmaker first learned of it Monday.
Democrats also circulated an email written by a Republican aide summarizing a list of changes that had been made in the legislation from an earlier version written last year. It contained no mention of abortion. 

The Associated Press contributed to this report.