It's a debate that has already sparked impassioned rhetoric and fierce partisanship, and shone a spotlight on an ideological hot topic with some cracks among parties and within parties. Senators will be forced to put their vote publicly on the record for the first time.
Republicans argue that this amendment is about protecting religious freedom. Democrats argue that the amendment is an assault on women's health.
In the spotlight is the Republican amendment, the "Respect Rights of Conscience Act," offered by Sen. Roy Blunt, R-Mo. It is a response to the White House's controversial contraception mandate. If passed, the amendment would allow any employer or any insurer in America to be given an exemption from covering contraception - or any service they choose - based on "religious belief or moral conviction."
"This is a fundamental matter of religious freedom and the proper role of our federal government. It's about who we are as Americans and renewing our commitment to the principles upon which this nation was founded," Sen. Kelly Ayotte, R-N.H., said in defense of the amendment. "Unfortunately, many have tried to characterize this amendment as denying women access to contraception. That's a red herring, and it's false. We are talking about government mandates that are interfering with conscience protections here that have long been ingrained in our law."
Republicans argue that this is about a faith principle that the first amendment guarantees, and point out that the word "contraception" is not mentioned once in the legislation.
Some conservative Democrats agree with this too. Sen. Joe Manchin, D-W.Va., announced this afternoon he will be voting for the amendment, saying that for him it "comes down to our religious liberties."
"I truly believe that we must safeguard Americans' right to exercise their sincerely held religious views, and I support this measure to protect that freedom of conscience," Manchin said in a statement late today.
But most Senate Democrats argue that the amendment is nothing more than "politics masquerading as morality," and is a "radical departure" that gives employers "broad discretion" to deny employees coverage. They argue this could put a woman's health at risk, with services including contraception, mammograms, pre-natal screenings, cervical cancer screenings, and potentially even flu shots not being offered.
"If this amendment passes, it would ban contraception coverage for any woman in America whose boss has a personal objection to it," Sen. Chuck Schumer, D-N.Y., said today. "The measure would force women to surrender control of their own health decision to their bosses. That concept is not merely quaint or old fashioned, it is dangerous and it is wrong."
Additionally, Democrats argue that the law is too broad and that it is hard to define what "religious" or "moral" issue could be that an employer could claim.
"Under the Blunt amendment, if an employer has a conviction against smoking they can refuse treatments for lung cancer or emphysema. If an employer says 'I don't approve of drinking and I refuse to cover any treatment program for alcoholism or substance abuse,' they could do it," Sen. Barbara Mikulski, D-Md., said today, "It puts the personal opinions of employers over the practice of medicine."
Democrats argue that this amendment would also go beyond women's health - that it would affect men, children and families as well. They argue that employers could limit access to childhood immunizations if they personally objected to them, or cut off coverage for prenatal care for children born to unmarried parents if they thought that was wrong.
Senate Majority Leader Harry Reid, D-Nev., has allowed the amendment to get a vote as part of an unrelated bill, the surface transportation bill, because he says it's clear Republicans will hold up the bill until this amendment is allowed a vote.
Leveraging Sen. Snowe's explanation for her retirement, Sen. Barbara Boxer said this is "Exhibit A" to show how Congress' polarization is slowing down legislating.
"We're on a transportation bill that's bipartisan, but the other side can't let it rest, can't let it go, can't move forward on it," said Sen. Barbara Boxer, D-Calif., "not only with this birth control amendment and women's health amendment, but with other amendments that have nothing to do with the subject. And it's what makes the American people think, what are we doing here?"
The amendment, which could be close, is not expected to pass but it does put many Senators - moderate Republicans and some Democrats - in a difficult and tricky position, having to go on the record with their vote on this for the first time.
Sen. Olympia Snowe, R-Maine, in an interview about her decision to leave Congress, said the amendment too broad for her, and she'd favor a narrower bill sponsored by Sen. Marco Rubio, R-Fla.
"I think it's much broader than I could support," Snowe said today, "I think we should focus on the issue of contraceptives and whether or not it should be included in a health insurance plan and what requirements there should be."