An unidentified individual this week filed an unfair labor practice complaint against Sen. Bernie Sanders Bernie SandersThe Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power Bernie Sanders: 'This is an election between Donald Trump and democracy' The Hill's 12:30 Report: Trump stokes fears over November election outcome MORE’s (I-Vt.) presidential campaign alleging illegal retaliation against staffers.

The complaint, filed on Monday with the National Labor Relations Board (NLRB), came amid a dispute between unionized field organizers for Sanders’s campaign and its management over wages that workers say fell below the senator’s long-touted $15-an-hour standard.

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While the Sanders campaign initially guaranteed its employees salaries equivalent to at least $15-an-hour, field staffers alleged that long hours had caused their wages to drop below that threshold.

That dispute was resolved on Tuesday after field organizers accepted an offer from the Sanders campaign to boost salaries to the equivalent of at least $15 an hour.

The unfair labor practice complaint mentions five alleged violations of the National Labor Relations Act, including improper retaliation against employees and the unlawful discharge of a staffer.

The full complaint has not yet been made public, but a summary of the allegations appears on the NLRB’s docket for July 22.

The Sanders campaign did not immediately respond to The Hill's request for comment. A spokesperson for the United Food and Commercial Workers Local 400, the union representing Sanders’s campaign staffers, said that the union was looking into the allegations, but declined to comment on the complaint.

Sanders’s campaign made history in March when it announced that it would become the first major presidential campaign to unionize.

The identity of the person who filed the complaint was not made public, but anyone can file a complaint with the NLRB, regardless of whether they have a direct connection to the alleged violations. The complaint will initiate a preliminary investigation by the NLRB’s branch in Indianapolis.

— Updated at 10:13 a.m.