A Bus Eireann driver was filmed "taking selfies and texting on Snapchat" on a Dublin route.
Footage taken by a passenger shows the driver appearing to tap and scroll on his mobile phone while driving the public bus.
The video is believed to have been taken on a recent journey from Westmeath to Dublin, and has been blasted by viewers as "disgraceful".
The passenger, who captured the clip but wishes to remain anonymous, told the Irish Mirror: "I got onto the bus and sat down and everything was normal until about two minutes after leaving the station he (the driver) pulls his phone out and starts going on to Snapchat.
"I'm pretty sure we were stopped the first time so I don't think much of it until I noticed him drifting into the other lane on the motorway and when I looked up he was on his phone.
"It was kind of terrifying how many times he had to seriously adjust the path of the bus while on his phone."
He added: "The bus driver was taking selfies and texting on Snapchat.
"He swerved at least five times, three of which were on back roads going pretty fast."
Social media users have shared their outrage about the video calling the drivers actions a "disregard for human life".
One user said: "So many lives at risk here," while another added: "Disregard for human life!"
Bus Eireann confirmed they are investigating the video.
A spokesman told the Irish Mirror: "Bus Éireann are aware of this footage and are currently investigating the matter.
"The safety of our passengers, staff and other road users is paramount to Bus Éireann.
"The use of mobile phones while driving is against the law.
"All of our drivers are trained to the highest standards and are expected to carry out their duties in a safe, professional and courteous manner.
"Any behaviour or misconduct which compromises the standards we expect is regarded as extremely serious and appropriate action is always taken.
"Depending on the nature of the misconduct, disciplinary action is taken with actions up to and including dismissal.
"We do not comment on individual cases."
