Debate opened Monday on Sen. Ben Nelson’s (D-Neb.) abortion amendment, launching what could be a contentious back-and-forth among Democrats as they look for unity on health care reform.

Nelson’s proposal, co-sponsored by Sen. Orrin Hatch (R-Utah), would prohibit federal funding under the legislation from being used for abortion procedures. Senate Majority Leader Harry Reid (D-Nev.) has said a vote on the measure could come this week.

Pro-abortion-rights Democrats are predicting it will fail. But Nelson, a leading moderate, has said he will not vote to end debate on the health care bill if his amendment — or something similar — is not included in the final package.

Nelson modeled his amendment after a proposal offered by abortion-rights opponent Rep. Bart Stupak (D-Mich.), which made it into the House bill with the help of Republican votes.