Unionized campaign organizers working for Sen. Bernie Sanders’s presidential effort are battling with its management, arguing that the compensation and treatment they are receiving does not meet the standards Sanders espouses in his rhetoric, according to internal communications.

Campaign field hires have demanded an annual salary they say would be equivalent to a $15-an-hour wage, which Sanders for years has said should be the federal minimum. The organizers and other employees supporting them have invoked the senator’s words and principles in making their case to campaign manager Faiz Shakir, the documents reviewed by The Washington Post show.

Sanders has made standing up for workers a central theme of his presidential campaigns — this year marching with McDonald’s employees seeking higher wages, pressing Walmart shareholders to pay workers more and showing solidarity with university personnel on strike. The independent from Vermont has proudly touted his campaign as the first presidential effort to unionize its employees, and his defense of the working class has been a signature element of his brand of democratic socialism and a rallying cry for the populist movement he claims to lead.