Labor representatives have expressed concerns to candidates publicly and to campaign staffs privately that a single-payer system could negatively affect their benefits, which in many cases offer better coverage than private plans. The change announced Wednesday would effectively give organized labor more negotiating power than other consumers would have under his plan by forcing employers to pay out any money they save to union members in other benefits.

One of the primary concerns union members and leaders have raised about Sanders’s Medicare-for-all plan is that they negotiated health-care coverage under the current system, in some cases ceding salary in exchange for those benefits.

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.