Julián Castro, one of the many 2020 Democratic presidential contenders, followed up on a pledge he made last year and endorsed his campaign staff's decision to join a union.

The campaign announced Thursday that its staff had affiliated with the Campaign Workers Guild.

“It’s not enough to talk the talk. You have to walk the walk,” Castro said on social media. “We are doing this at every step of this campaign. I’m proud to announce that my campaign staff has unionized.”

Bernie Sanders’ campaign announced Wednesday that its workers had signed a union contract that will pay $20 an hour. They affiliated with United Food and Commercial Workers Local Union 400. His staff started working to unionize as soon as the campaign started.

Castro, former secretary of Housing and Urban Development under President Barack Obama, had said in January he would pay his workers $15 an hour and support any of his workers' efforts to unionize. Campaign spokesman Sawyer Hackett said in a statement that Castro also was the first to create a staff manual with a strong sexual harassment policy.

Former Vice President Joe Biden’s campaign told The Associated Press Thursday that he would welcome the campaign forming a union. But his campaign said it would offer good pay and benefits to make unionizing unnecessary

Candidates' support of their workers' unionizing follows demands from campaign staffers for Democrats to practice the pro-worker rhetoric they’ve preached.

Stagnant wages, pay inequity, shrinking benefits, fewer work hours and, in some parts of the country, how trade affects jobs are some of the key issues in the 2020 election.

Union support also is critical in elections, particularly for Democrats. But only 11.6 percent of full-time workers and 5.4 percent of part-time workers were union members in 2018, according to the Bureau of Labor Statistics.

In March, Castro attended a meeting of campus workers at Stanford, his alma mater, to show support before they began contract negotiations with the university. He spoke of raising the national minimum wage to $15 an hour and of picking appointees to his Cabinet and the National Labor Relations Board that are sensitive to workers' plights, according to a report in the Stanford Daily.

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