Vermont Sen. Bernie Sanders' proposal to move all Americans to a single government plan has had an ongoing problem with a constituency that should be among his core supporters: organized labor.

The issue is that like most other Americans, union workers like their current plans and want to keep them. As healthcare costs have risen over time, unions have negotiated collective bargaining agreements in which they accepted lower salary increases in exchange for more generous health coverage. Now, the Sanders plan would require taking them away, and they are not happy about it.

Sanders appeared at a labor town hall event on Monday and drew some heat on the issue. Now, the Washington Post reports that he has made a change to his plan:

Under Sanders’s new wrinkle, those unions could renegotiate their contracts under the supervision of the National Labor Relations Board. 'Unions will still be able to negotiate for and provide wrap-around services and other coverage not duplicative of the benefits established under Medicare-for-all,' the plan now says, a seeming acknowledgment of a role for private coverage by a campaign that has railed against others for not taking a hard-enough stance against such plans.

On the surface, the change does not appear to do much to alter the plan. After all, under the legislation as it existed before the change, employers were still theoretically free to offer coverage that did not offer any of the same benefits that were in the new government plan. However, the issue has always been that because Sanders promises that the government plan will cover such a wide array of benefits (listed here), in reality it effectively outlaws private coverage. Sanders often likes to say that his plan would allow for coverage of cosmetic surgery, but as Margot Sanger-Katz helpfully detailed over at the New York Times, cosmetic surgery insurance does not actually exist.

That said, the article also cites a Sanders adviser as saying that the change "is meant to guarantee that any savings to employers under the Medicare-for-all plan 'must be passed on to their organized workers in the form of additional wages or benefits.'" That suggests that as the result of the arbitration process, union workers will be treated differently than non-union workers.

That smacks of unfairness. The whole moral pitch for the Sanders plan, and for his candidacy in general, is that it's supposed to create more equality and end special interest deals. But by treating union workers differently, he'd be making exceptions for a powerful liberal constituency whose votes he needs.

There are plenty of low-income and middle-class workers who are not unionized. While union healthcare plans may be especially generous, all workers who have insurance through their employers — which includes about half the country — in some way have accepted lower salaries because businesses provide them with health benefits. Even if it wasn't the result of a formal collective bargaining process, this is the simple reality given that businesses budget in terms of overall compensation.

It should be recalled that a special carve out for union plans nearly killed Obamacare. Initially, Obamacare's Cadilac tax of expensive healthcare plans was supposed to go into effect much sooner, but with a special provision that delayed its effect for generous union plans. Opponents cited this as one of the special interest deals, and it nearly smothered the efforts to pass the bill. Eventually, Democrats were forced to delay the taxes for everybody. Sanders, if he ever gets much further in the election process, risks a similar sort of backlash.

At the end of the day, if Sanders and others are serious about transitioning everybody to a single government plan, they need to make the case that unions, like many other groups, will have to suck up the rocky transition to get to what they believe is a better place. He can make the case that once it's in place, employers will be saving money on insurance costs, so salaries will start to go up. But it is simply an untenable position to adopt a special carve out for his preferred special interests.