A union has threatened legal action against Stagecoach after it cancelled bus drivers' holiday dates during planned strikes.
Unite union members in the south and west of Scotland are set to walk out for seven days over three weeks in May in a dispute over pay.
The union said described the cancellation of holidays as a "significant escalation", and said it planned to seek a legal order banning the move.
Stagecoach said postponing annual leave was necessary due to increasing staff sickness levels and to provide "dependable services to customers".
BBC Scotland News has seen a letter sent to a Stagecoach employee informing them that two weeks of agreed holiday in May has been cancelled.
It said the leave dates would be rescheduled "at a time that can be accommodated by the operational needs of the business".
The letter also said failure to attend work could be considered gross misconduct and "may lead to disciplinary action".