The Government is being urged to review the rules on civil servants speaking at public events after a transport official sparked outrage over comments about train drivers.
Peter Wilkinson, director of rail passenger services at the Department for Transport (DfT), faced calls for his resignation after telling a meeting in Croydon, south London, that drivers who resist changes to their working hours can "get the hell out of my industry".
Trade unions reacted with anger after he warned there would be be "punch-ups" with train drivers over plans to change working hours.
Mr Wilkinson issued a statement on Monday night which said: "I apologise for any offence caused by my comments."
Louise Haigh, shadow Civil Service minister, has tabled a question in Parliament to the Cabinet Office and the Transport Department in the wake of the controversy.
She said: "Trust in the Civil Service - in its impartiality and its competence - is essential. That's why it is astonishing that a senior civil servant could behave in such a partisan and vitriolic way in what appears to be a breach of the Civil Service Code.
"I've written to the Cabinet Office asking them to urgently review the rules around civil servants attending events organised by Government MPs, and to reassure the public that the Civil Service ultimately serves the public and not the Conservative Party."
A Department for Transport spokesman said: "It is right that Peter Wilkinson has apologised for his comments. He has a fine record of delivering a better railway for passengers, and this is what he will continue to do."