The Royal Mail is seeking an injunction to prevent staff going on strike during the crucial Christmas trading period and the general election next month.
The postal service has taken legal action against the Communications Workers Union (CWU), claiming there were “potential irregularities” in a recent ballot for industrial action.
Royal Mail alleges that CWU officials interfered with the voting system by intercepting postal ballot papers, instructing members to vote in favour of strike action and pressuring workers to make their vote public.
CWU said it “completely rejects and denies this claim in the strongest terms”.
The motion to strike was passed by more than 97% of union members. Posties have accused Royal Mail of failing to live up to an agreement reached last year over a raft of issues, including pay and conditions.
If Royal Mail is successful in obtaining an injunction, CWU will not be able to strike until another vote is held, which could delay industrial action until after the 12 December general election.
In a statement Royal Mail said: “The company is making this High Court application because the integrity and legal soundness of any electoral process is vital.
“This is particularly the case in relation to potential industrial action around the general election on 12 December 2019.
“Royal Mail is also making this application because of the damage industrial action would do to the company and its customers in the run-up to Christmas.”
CWU general secretary Dave Ward said: “It will be clear to all our members and everybody connected with Royal Mail and this dispute, that the chief executive and his board will go to any lengths to deny the democratic mandate of our members to stand together and fight for their future and the very future of UK Postal Services.”