LAS VEGAS — Bernie Sanders’s pitch on “Medicare for all” was partially drowned out by protesters during a speech at a union event.

On Tuesday, after the Vermont senator, 77, received a question from a Frontier Communications employee about if his plan would change her healthcare coverage, members of the audience began cheering and clapping in support. In the middle of his response, roughly a dozen members of the Culinary Workers Union Local 226 began chanting “union healthcare, union healthcare” in protest.