Independent Sen. Bernie Sanders of Vermont has endorsed what he calls an “important” citizen-initiated referendum in nearby Portland, Maine, telling supporters in an email Thursday that the city “has the potential to pass the most progressive, inclusive minimum wage initiative in the history of the United States.”

“A ‘Yes’ on Question D would raise the minimum wage for all workers to a living wage of $18 an hour—including tipped workers, workers with disabilities, youth, gig workers, and incarcerated workers,” Sanders wrote. “As you might expect, opposition from the billionaire class and the ultra-wealthy to Question D has been fierce.”

“Lobbyists like the National Restaurant Association, large corporations like Uber and Doordash, and real estate developers have collectively poured more than $600,000 into Portland on mailers, advertising, and misinformation campaigns,” Sanders continued, “all so they can continue to pay restaurant workers and gig workers subminimum wages.”

“As a result of their efforts, polling shows a very tight race,” he added. “And with only a few days to go until the vote is decided, it’s up to our progressive movement in Maine to stand together and fight to pass Question D.”

The Portland Press Herald reported that the proposal “was put on the ballot by the Maine chapter of the Democratic Socialists of America’s Livable Portland campaign, which has said it’s expected to raise wages for about 22,000 workers across the city.”

“Sanders is the latest in a flurry of last-minute endorsements secured by One Fair Wage, a national group focused on eliminating subminimum wages that allow certain workers, such as restaurant servers, to earn less than the standard minimum wage,” the newspaper noted. “Saru Jayaraman, president of One Fair Wage, said the senator has been working with that organization for years on minimum wage issues.”

Sanders urged voters to sign a petition in support of the ballot measure. Those who do so are redirected to the Maine voter information lookup service, where they can confirm their polling location.

The federal minimum wage of $7.25 per hour has remained stagnant since 2009 and provides only a fraction of what a full-time worker needs to afford a modest one-bedroom rental home in the United States. The federal subminimum wage of $2.13 per hour for tipped workers has not been raised since 1991.

According to the National Low-Income Housing Coalition, a full-time worker would need to make $17.74 per hour to afford a one-bedroom apartment in Maine, meaning the statewide minimum of $12.75 ($6.38 for tipped workers) and Portland’s current minimum of $13 ($6.50 for tipped workers) are inadequate. If Portland voters approve Question D during the November 8 midterms, the city would have an $18 hourly wage floor.

“At a time when half of American workers are living paycheck to paycheck, and millions of people earn starvation wages and struggle to put food on the table, the wealthy and powerful have never had it so good,” wrote Sanders.

The Vermont progressive expanded on that point Friday in a Fox News op-ed modeling the kind of anti-corporate profiteering and pro-working class messaging he would like to see prioritized by the Democratic Party, with which he caucuses.

“What we are seeing all across the country and in every sector of our economy is that working people are standing up in the face of corporate greed, demanding fairer wages, better working conditions, and the dignity and respect on the job that they deserve,” Sanders wrote in his Thursday email.

“Our greatest weapon in this fight is solidarity,” he concluded. “The people of Portland, Maine have an incredible opportunity this Tuesday to continue our movement’s collective struggle by voting ‘Yes’ on Question D.”