A former campaign employee from the 2020 presidential bid of Sen. Bernie Sander filed a labor complaint this week, alleging that some employees faced retaliation for involvement in organizing for a collective bargaining agreement.

The employee, who has not been publicly identified, filed the complaint with the National Labor Relations Board (NLRB) on Tuesday, according to a redacted copy of the charge obtained by Bloomberg Law.

The complaint alleges that Sanders’ campaign made unionized employees work additional days without commensurate days off, thus violating the terms of their collective bargaining agreement.

Campaign management "retaliated against me when I organized the bargaining unit and sent an email requesting compliance with the [collective bargaining agreement],” the individual wrote in the charge.

The charges, if true, could be yet another ironic blow for the self-proclaimed Democratic socialist senator, I-Vt., who has portrayed himself as an ally of organized labor.

Sanders made history earlier this year after announcing that his campaign employees would be represented by a union. But The Washington Post reported last week, that campaign staffers have been “battling with … management, arguing that the compensation and treatment they are receiving does not meet the standards Sanders espouses in his rhetoric, according to internal communications.”

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An agreement on that dispute was reached earlier this week, with Sanders announcing that pay would be raised from $36,000 to $42,000.

The unfair labor practice charge filed on Tuesday alleges that some employees were not notified of their collective bargaining agreement before being hired and made to believe they were “at-will.”

“The campaign leadership, from Senator Sanders on down, respects the rights of all of its employees to speak collectively and bargain about their terms and conditions of employment, and it supports the mission of the NLRB to enforce worker and union rights," Sanders' campaign said in a prepared statement to Fox News. "That is exactly why the Bernie 2020 campaign voluntarily recognized the employees’ chosen union and engaged in good faith bargaining that resulted in a historic collective bargaining agreement."

The campaign declined to discuss the specifics of the matter "in order to maintain the integrity of the NLRB process."

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The NLRB’s office in Indianapolis is now investigating the allegations, The Hill reported. If the claims are proved to be true, and if the National Labor Relations Act and involved parties are unable to bring about a resolution, the case will be sent to an NLRB administrative law judge.