The Johns Hopkins University graduate student workers’ union filed an unfair labor practice charge to investigate the private Baltimore university less than three months after reaching a contract agreement.

In a Thursday news release, Teachers and Researchers United, or TRU, said the university illegally established new work requirements for Ph.D. workers as retaliation for their “historic” contract won in April. Members of the union include students who work or conduct research while earning their Ph.D.s.

The unfair labor practice charge, filed with the National Labor Relations Board, seeks to investigate “mandating increased workloads, rescinding offers for appointments, and explicit statements by management that blame the union for these illegal changes,” the release says.

The union also alleges that the university illegally threatened to withhold pay from workers and failed to enact contract processes.

According to an email from the union’s account, since ratifying the contract in April, “our members from across the University have brought to our attention instances where the University has been trying to implement measures in bad faith in order to recoup their losses and punish workers.”

A spokesperson for Johns Hopkins University said the university is aware of the charge and will follow the National Labor Relations Board process to address it.

“The University has acted consistently with the collective bargaining agreement and will continue to do so. The CBA has specific language which authorizes the University to make work assignments,” the spokesperson said in a statement.

Under the contract, a grievance procedure allows the union to bring issues of contract violations directly to the university, TRU said in the email. In addition to the charge, the union has filed several cross-departmental grievances and hundreds of members are involved.

The university spokesperson said that a grievance filed by the union directly with Hopkins is working its way through the process established under the collective bargaining agreement.

“Departments across the University are implementing additional workload requirements not because they are required to, but because they are choosing to,” Stacy Lu, interim steward in the union said in the release. “These changes are messing with our literal livelihoods.”

Once the union receives an assigned investigator from the National Labor Relations Board, it will provide the board with instances of any violations of the National Labor Relations Act and a hearing will be scheduled, according to TRU.