Stagecoach Supertram is urging the Unite union to call off a planned strike in Sheffield.
The strike over the de-recognition of one of the union's representatives is scheduled to take place for an "indefinite" period from 16 August.
The union said Stagecoach's decision to no longer deal with the official was felt by some members to be "drastic".
Stagecoach said its "door remained open" for talks with Unite to try and resolve the issue.
Unite members voted in favour of strike action in a ballot.
It was called after Stagecoach Supertram said it could no longer deal with the Unite official, claiming he had "broken an agreement" on standards.
The company said: "The people do not want to see completely unnecessary disruption to their tram services.
"It is extremely disappointing that the union seems determined to press ahead with strike action, which will also hit the pockets of many of our employees' families."
They added that they were getting together contingency plans for services in the event of a strike, but were hopeful that they would still be able to run a "significant tram service".
John Evans, from Unite, said: "We've had a good working relationship with the company over the years but unfortunately there's been a problem with this particular individual.
"There was certainly an issue that needed to be dealt with... the action that they have taken is thought to be a little bit drastic."
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