Lawmakers on the Senate Finance Committee will likely vote Thursday on an amendment that would require employees to offer their workers health insurance.

The proposal, sponsored by Sens. John Kerry (D-Mass.) and Jeff Bingaman (D-N.M.), would mandate that large employers must insure their workers or pay a $750 fine for every full-time employee or $375 for every part-time employee without coverage. It would also prorate the fee based on the number of months an employee remained uninsured, and it would index that scale according to the Consumer Price Index starting in 2013.

Kerry and Bingaman's proposal would also scrap the Finance bill's "free rider" provision -- a fee on employers whose workers receive subsidies from the federal government.

Debate over the amendment on Thursday is likely to be thorny. A number of Democrats have long criticized Sen. Max Baucus' (D-Mont.) healthcare bill for its lack of strong employer mandate, insisting that its "free rider" provision could discourage firms from hiring low-income workers eligible for federal health insurance assistance.

But Republicans resist an employer mandate of any kind. Among other qualms, they seem to agree with the U.S. Chamber of Commerce's argument that any such requirement would impose hefty fees on small businesses that they cannot handle in the current economy.

Thursday's outcome, however, is perhaps only a preview of what is to come. The Senate Health, Education, Labor and Pensions Committee did include an employer mandate in its final reform bill. When the Finance Committee merges its effort with the HELP panel's work, the employer mandate question will come up once again.