WASHINGTON — Bernie Sanders' presidential campaign said Wednesday that it is the first in history to ratify a union contract with workers.

Sanders' staffers voted to unionize shortly after he entered the 2020 presidential race two months ago, and the Vermont independent senator said he supported the effort. The staff has affiliated with United Food and Commercial Workers Local 400.

"We are proud of our workers and proud to uphold Bernie's commitment to collective bargaining rights and a strong labor movement," Sanders campaign manager Faiz Shakir said. "Together, we have achieved some of the strongest standards for campaign workers in history and set the bar higher for the next generation of campaigners."

The collective bargaining agreement includes provisions for pay equity and transparency, coverage for mental health care, standards for campaign staffers lodged in supporters' homes and an arbitration process for worker grievances, among other provisions. The campaign is already providing for health care and other basic employee benefits.

The campaign also announced that it had implemented new workplace guidelines to combat sexual harassment and discrimination and ensure diversity after numerous women came forward to say they had negative experiences during Sanders' 2016 presidential bid.

The unionization effort fits with Sanders' pro-labor political message, but it also comes as campaign staffers everywhere have begun demanding better treatment — especially from Democrats who they say don't always practice what they preach when it comes to workers.

Last year, at least 25 congressional and other campaigns, along with three state Democratic parties and a handful of progressive groups, ratified collective bargaining agreements with the Campaign Workers Guild, a new union for political workers that launched in early 2018, while more affiliated with other unions.

Campaigns are far from traditional workplaces and some political workers say bosses take advantage of their idealism to underpay and overwork them, and to make sure they stay quiet about problems, such as sexual harassment.

How candidates treat their own staff has become a political issue in the 2020 presidential primary, with candidates touting that they will, for instance, pay interns $15 an hour as a way to show their commitment to progressive ideals.

Some other 2020 Democratic candidates have also said they would support their staff if they chose to unionize.