A public inquiry is to be launched into the way transport giant Stagecoach has behaved during Preston's bus wars.
The probe by North West Traffic Commissioner Beverley Bell will "look into its conduct as an operator."
But today Stagecoach said it was angry about the action being taken against it.
The announcement was made by transport minister Rosie Winterton in Parliament on Tuesday, raising the temperature of a dispute which has raged between Stagecoach and Preston Bus since May.
A spokesman for the traffic commissioner said she had decided to call the inquiry after "weighing up what she has been told" and deciding she "needs to air it in public and get to the bottom of the situation once and for all."
Stagecoach will be forced to publicly defend itself against accusations that it is attempting to run rival firm Preston Bus off the road.
Representatives from the national firm will be questioned and the inquiry is due to hear evidence regarding Stagecoach's behaviour.
It is also likely that Preston Bus employees will be called to give evidence.
If the traffic commissioner sees fit she can either reprimand, fine or have the ultimate power to take away Stagecoach's licence to operate services.
A preliminary hearing will be held on December 18 and will set out the timetable for the inquiry. The full inquiry will be held in February and no venue has yet been set.
A Stagecoach spokesman said: "We are angry about the untrue allegations that have been made about our business and we will be making a robust defence of our position at the public inquiry."
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