“We’re aware that Unite is balloting drivers employed by the tram operator, KeolisAmey Metrolink, over industrial action,” said Danny Vaughan, TfGM’s chief network officer.

He said: “We are meeting with both KAM and Unite this week to understand the issue and any concerns in more detail.

“We are keen to work with both parties to resolve the issue without causing disruption for passengers.”

KeolisAmey Metrolink said that while its rosters “already align with safety standards” it wanted to make “ongoing sustainable improvements” for its drivers.

“Driver welfare and managing fatigue are key priorities for us,” said Damien Chabas, managing director.

“Our focus has been on meaningful consultation and finding balanced solutions that are viable for the long term sustainability of Metrolink and that support the delivery of a safe and reliable service for passengers.”