During a recent interview with Sean Hannity of Fox News, Sen. Marco Rubio, R-Fla., picked up a talking point that had been widely repeated in the conservative blogosphere about workers at the Internal Revenue Service wanting to get out of Obamacare.

Referring to President Barack Obama’s health care law, Rubio said, "Even the employees’ union for the IRS -- the very people in charge of enforcing this law -- are begging to be let out from under this law."

Since federal-employee unions tend to be some of Obama’s staunchest supporters, it would be unusual if the National Treasury Employees Union had turned against the president over his signature legislative accomplishment. Is that really what happened?

There’s a kernel of truth here, but the episode is considerably more nuanced than Rubio, or most of the other commentators, let on.

The union wasn’t lobbying against Obamacare per se, but rather against a bill sponsored by one of the law’s opponents that would change how Obamacare operates. (You can read the union’s form letter here .)

This is a complicated tale, so we’ll start at the beginning.

When the health care law was being written in 2009 and 2010, Republicans proposed requiring lawmakers and their staffers to obtain insurance through the exchanges, arguing that if the law was good enough for ordinary Americans, then it was good enough for the people in Congress who wrote the law. Presumably fearing a public backlash if they refused, Democrats accepted the language, and it became part of the law.

But as the New York Times recently put it, the provision "has been a headache for many in Congress ever since." That’s because the law does not include an explicit mechanism to allow the federal government to pay its employer share of congressional employees’ health insurance if they use the exchanges.

For most Americans with employer-based insurance, including government employees, the employer pays a majority of the cost of insurance, lessening the financial burden for employees. Unless a fix can be found, congressional employees will have to foot the entire cost of their health insurance when buying insurance on the exchange -- a financial hit that could go well into the thousands of dollars.

Despite longstanding concerns about the provision’s impact, neither Congress nor the administration has yet come up with a workable solution, although the administration promises action in time for the opening of the exchanges this fall.

However, after word leaked to Politico in April that congressional leaders in both parties were "engaged in high-level, confidential talks" to rescind the provision, U.S. Rep. Dave Camp, R-Mich., decided to offer a bill that would expand the mandate to use the exchanges beyond Congress to the president, vice president and all federal employees.

As of this writing, the bill had not advanced to a committee hearing. Still, the fact that the bill was introduced at all set off alarm bells at the National Treasury Employees Union, which represents 150,000 employees in 31 federal agencies and departments. That includes the IRS, which has a role in enforcing the tax penalties for failing to secure health coverage.

This is why the union has urged its members to oppose Camp’s bill.

In a statement to PolitiFact, union president Colleen M. Kelley called Rubio’s claim "a misrepresentation."

She said the union’s beef is not with Obamacare itself, and the episode does not represent a policy rift between the union and Obama. Rather, the union is concerned that an opponent of Obamacare wants to change the law, effectively uprooting 150,000 of its members from their existing plans and potentially leaving them to pay the entire cost of their health insurance without employer assistance.

When we checked with health policy experts, most said they don’t blame Rubio for seizing on a juicy dispute among longtime allies, but they agreed that the actual story is a lot more complicated.

Obama and his allies created a system in which most Americans -- at least three quarters -- who had insurance would remain on their existing plans and would see few if any disruptions from the new law. The exchanges were created to provide a marketplace for Americans who lack insurance entirely or have to buy insurance on their own.

By contrast, Camp’s bill would force federal employees out of their longstanding coverage and into a new system.

An added irony is that the Federal Employees Health Benefits Program is widely considered a key model for the exchanges themselves. Under the program, federal employees under the age of 65 can choose among a variety of health insurance offerings, just as people will be able to do under the exchanges. In 2003, the conservative Heritage Foundation published a paper touting the program as a model for market-based health care reform.

"The union is correct that the primary purpose of the ACA is to provide a marketplace for the sale of health insurance for those who do not have such coverage, which would of course exclude IRS and other government employees," said Gail Wilensky, the former head of Medicare and Medicaid under President George H.W. Bush. In fact, she said, "Federal employees, unlike most other employees, have been offered a wide variety of plans through the FEHBP program and are probably the least likely to want to leave their present" coverage.

Our ruling

Rubio said that "even the employees’ union for the IRS -- the very people in charge of enforcing this law -- are begging to be let out from under this law." He has a point that the National Treasury Employees Union has asked its members to oppose efforts to force its members into the exchanges created by Obama’s health care law. But he ignores a lot of context that would give a listener a different impression.

The union’s quarrel is not with Obamacare itself, but rather with efforts by the law’s opponents to uproot federal employees from their longstanding health plans, a change the union views as punitive. By contrast, Obamacare was written to keep as many Americans as possible on their existing insurance plans, with the exchanges envisioned as a way for people without insurance or with inadequate insurance to purchase a plan. On balance, we rate the claim Mostly False.