Bernie Sanders' 2020 presidential bid is reportedly going through internal turmoil over staff complaints that the campaign isn't paying the equivalent of the $15 an hour wage that Sanders has backed as a federal minimum.

The Vermont senator has long advocated a federal minimum wage of $15, and has touted his status as the first major presidential candidate to have a unionized campaign staff.

Internal campaign emails obtained by the Washington Post showed that several field organizers contacted the campaign on July 11 to complain that they were underpaid. "I am struggling financially to do my job, and in my state, we’ve already had 4 people quit in the past 4 weeks because of financial struggles,” the story quoted one stating. The messages were sent during a online social media event set up by the campaign to address internal staff matters.

The Sanders campaign reportedly pays its field organizers not on an hourly basis but with a flat annual salary of $36,000. That is the equivalent of a little more than $17 an hour for a 40-hour week, but presidential campaigns typically require their worker to put in hours far in excess of that. Staffers have complained that that workload drags their average pay down bellow $15 a hour.

“As union members, the Bernie 2020 campaign staff have access to myriad protections and benefits secured by their one-of-a-kind union contract, including many internal avenues to democratically address any number of ongoing workplace issues, including changes to pay, benefits, and other working conditions,” United Food and Commercial Workers Local 400, the New Hampshire-based union that represents Sanders campaign staffers, said in a statement. A spokesman for the union declined to comment on ongoing talks between the union and the campaign.

UFCW Local 400 previously told the Washington Examiner that it was advocate solely for the campaign's workers, not the campaign itself, and has not ruled out strikes or other measures should they become necessary.

The Sanders campaign did not respond to a request for comment. "We know our campaign offers wages and benefits competitive with other campaigns, as is shown by the latest fundraising reports," campaign manager Faiz Shakur told the Post. He added, "Bernie and I both strongly believe in the sanctity of the collective bargaining process and we will not deviate from our commitment to it."

Sanders slammed Senate Majority Leader Mitch McConnell on Thursday for not setting a floor vote on the $15 federal minimum wage bill that passed the House Thursday. "Mitch McConnell is wrong. Since 1979, when a state has increased the min. wage, employment and wages typically go up, not down," Sanders said. "A $15 minimum wage would raise wages for 39 million people and lift millions of Americans out of poverty. Why is McConnell afraid to let us vote on it?"