The company says it's treating the matter seriously.
Bus Éireann says it's aware of a video of a bus driver using a mobile phone while driving in the midlands and is investigating.
The online footage was filmed by a passenger on the Westmeath to Dublin Route.
The company says the safety of its passengers and other road users is of "paramount importance" and drivers are expected to carry out their duties in a safe, professional and courteous manner.
It's treating the matter seriously and will take disciplinary action up to and including dismissal pending the outcome of the investigation.
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