Engineers at First Group Glasgow say that industrial action is "increasingly likely" after being unable to come to an agreement with the transport giants.
Months of negotiations between the bus firm and Unite, the union representing the 148 workers, have resulted in a stalemate between the two parties, prompting them to vote on strike action. Should the result of the vote on July 9 be in favour of a walkout, the employees will most likely hold the stoppage during the Commonwealth Games,
Unite Regional Industrial Officer Eddie Duffy said: "First Glasgow management are treating their long-serving workforce with complete and utter contempt - they could and should have settled this basic pay issue months ago."
Talks between bus workers and their bosses stalled following the almost unanimous rejection of a 1.2% pay rise.
Fiona Kerr, managing director of First Glasgow previously questioned the union's ability to represent its members after they rejected the pay deal despite recommendations to accept it.
Mr Duffy said: "Unite is doing everything it can to resolve this dispute but the threat of action affecting First services during the Commonwealth Games is now a very real prospect."