Presidential candidate Sen. Bernie Sanders has pledged to American workers that he would institute a $15-per-hour minimum wage if he wins the White House in 2020.

But unionized workers on Sanders’ own campaign say they wish he would start now -- by paying a higher wage to them.

According to a report, members of Sanders’ staff have been using the senator's own campaign rhetoric against him as they try to wrestle more pay from the self-described democratic socialist.

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In a letter to Sanders campaign manager Faiz Shakir, the campaign staffers claim they “cannot be expected to build the largest grassroots organizing program in American history while making poverty wages,” the Washington Post reported.

“Given our campaign’s commitment to fighting for a living wage of at least $15.00 an hour,” the letter continues, “we believe it is only fair that the campaign would carry through this commitment to its own field team.”

“Given our campaign’s commitment to fighting for a living wage of at least $15.00 an hour, we believe it is only fair that the campaign would carry through this commitment to its own field team.”
— Letter by Bernie Sanders campaign staffers

According to the Post, field organizers claim that their long hours working on behalf of Sanders drop their actual pay to about $13 per hour.

“Many field staffers are barely managing to survive financially,” the union letter says, “which is severely impacting our team’s productivity and morale. Some field organizers have already left the campaign as a result.”

“Many field staffers are barely managing to survive financially, which is severely impacting our team’s productivity and morale. Some field organizers have already left the campaign as a result.”
— Letter by Bernie Sanders campaign staffers

But when contacted by the Post on Thursday, Shakir seemed to paint a different picture.

“We know our campaign offers wages and benefits competitive with other campaigns, as is shown by the latest fundraising reports,” Shakir said in a statement, according to the Post. “Every member of the campaign, from the candidate on down, joined this movement in order to defeat Donald Trump and transform America. Bernie Sanders is the most pro-worker and pro-labor candidate running for president.”

“Every member of the campaign, from the candidate on down, joined this movement in order to defeat Donald Trump and transform America. Bernie Sanders is the most pro-worker and pro-labor candidate running for president.”
— Faiz Shakir, Sanders campaign manager

As for Sanders himself, the Post said it was unclear whether the candidate was aware of the grievances among his campaign staff.

The Post report surfaced on the same day that the Democrat-controlled House voted in favor of a bill to gradually raise the federal minimum wage to $15 per hour. The current federal minimum wage is $7.25 per hour, unchanged since 2009.

The situation in the Sanders campaign seems a far cry from March, when Sanders’ campaign proudly announced that its employees had chosen to be represented by the United Food and Commercial Workers Local 400. In May, the campaign ratified a union contract with the workers, making it the first presidential campaign in history to do so.

At the time, the campaign touted "unprecedented standards for campaign workers," including pay transparency, a defined wage scale, access to mental health care coverage, an anti-discrimination policy that protects immigrant and transgender staff members, and a "pro-worker grievance and arbitration process.”

Meanwhile, President Trump has offered a different perspective on conditions facing U.S. workers.

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During a campaign rally in Greenville, N.C., earlier this week, the president said 6 million new jobs had been created in the U.S. since he was elected and the nation’s unemployment rate of 3.7 percent was at its lowest point in decades.

Republican leaders have said a minimum wage hike would be “devastating” for middle-class families, citing research from the Congressional Budget Office. The CBO report found that the Democrats’ bill would boost wages for about 17 million people – but it would also reduce business income, raise consumer prices and reduce the nation’s output. Overall, the CBO said the move would reduce real family income by about $9 billion in 2025 – or 0.1 percent.

Fox News’ Ronn Blitzer and Fox Business’ Brittany De Lea contributed to this story.