Sen. Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.) on Sunday joined striking AT&T workers in Louisville, Ky., ahead of a presidential campaign rally.

The event Sanders joined was one of several across nine states involving 20,000 workers who are protesting labor practices at AT&T.

ADVERTISEMENT

Communications Workers of America has filed an unfair labor practice charge with the National Labor Relations Board (NLRB) against AT&T for not bargaining in good faith, according to local station WLKY.

“A strike is in no one’s best interest. We remain ready to sit down with union leaders to negotiate a new, improved contract for our employees," AT&T said in a statement reported by WLKY.

Sanders has long been a proponent of workers' rights and last week released a plan aimed at increasing union membership.

The strategy dubbed the “Workplace Democracy” plan sets a target of doubling union membership during Sanders's first term if elected.

Under the plan, the NLRB would be able to certify a union if a majority of eligible workers consent and enact “first contract” provisions that order employers to start negotiating within 10 days of receiving a request from a new union.

Sanders on Monday was endorsed by United Electrical Workers, the second major union to put its support behind a Democratic nominee.

Former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE scored an endorsement from the International Association of Fire Fighters earlier this year.