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Bernie Sanders was endorsed by the American Postal Workers Union Thursday

The postal workers backing comes as Sanders' aides fretted Clinton's union support

Washington CNN  — 

Bernie Sanders’ push to let post offices offer banking services – which supporters say would help poor and rural Americans – may have just won him his biggest union endorsement yet.

The American Postal Workers Union announced their endorsement of Sanders Thursday, giving the insurgent Democratic candidate a small boost at a critical moment as his campaign tries to find its way.

While the novel idea wasn’t the only reason the postal workers got behind Sanders, union president Mark Dimondstein said it was important.

“That’s something we’ve been working on for a period of time,” Dimondstein said. “It’s very important from this standpoint: we not only want to preserve the public post office we want to enhance it.”

Sanders touted the idea in an interview with Fusion last month.

“I want to see our post office be reinvigorated. And one of the ways that I think we can help not only the U.S. Postal Service, but help a lot of low-income people – if you are a low-income person, it is, depending upon where you live, very difficult to find normal banking,” Sanders said last month. “Banks don’t want you. And what people are forced to do is go to payday lenders who charge outrageously high interest rates. You go to check-cashing places, which rip you off. And, yes, I think that the postal service, in fact, can play an important role in providing modest types of banking service to folks who need it.”

The postal union brings with it more than 200,000 members at a time when Sanders and Clinton are scuffling behind the scenes to win over organized labor.

Clinton scored a big win late last month when the American Federation of State, County and Municipal Employees – with its 1.6 million members, picked her over Sanders. That added to an early endorsement for Clinton from the American Federation of Teachers, whose president, Randi Weingarten, Clinton has long been close with.

Two other issues which won Sanders the postal workers’ support: backing of postal union reform and opposition to postal privatization.

Related: Bernie Sanders scores nurses’ union endorsement

Sanders’ campaign welcomed the endorsement on Thursday.

“APWU is everywhere there is a post office and their 250,000 members are way at the top when it comes to member involvement and union democracy,” said Larry Cohen, Sanders’ senior adviser on labor issues. “We welcome the unprecedented support of the APWU executive board and look forward to working with their members across the United States.”

In the Democratic primary process, national union endorsements bring money and organization to what can be a grind-it-out political process. After the AFT endorsed Clinton, their members – sporting blue shirts emblazoned in their logo and the Clinton logo – were seen across the country. The same was true for the National Nurses United, Sanders’ first national union endorsement.

“Given his life-long commitment and continued commitment to the organized labor moment, we would like to have as many organized labor endorsements as we could get,” Jeff Weaver, Sanders’ campaign manager said on Wednesday, before the postal endorsement was announced. “Sen. Sanders has been standing by unions when the cameras aren’t there. People know that. That word of mouth goes through the union membership.”

Weaver, disparaging the way national unions don’t always match what their members want, added, “Washington has a certain culture and people in Washington are not always in sync with the people down below.”