She urged the company to come up with a robust plan to resolve the issues, including seeking help from the council and Scottish Government to fill the staff voids.
Ms White referenced instances of children being left stranded in the cold while others are struggling to do their food shopping due to the repeated cancellations.
In a response to Ms White, Stagecoach said its Arbroath depot, responsible for operating the X7 service, is currently 25 drivers short which equates to 17 per cent of its workforce.
Its managing director for the East of Scotland, Douglas Robertson, added that staff sickness has also contributed to the “substantial” disruption.
The company said it has tried to loan drivers to the north-east from other parts of Scotland but “it is not always possible”.
In his reply to the MSP’s letter, Mr Robertson said: “There is no doubt that we have been facing some substantial difficulties over recent months in providing our usual standard of service delivery.
“This is due to several issues that having been ongoing.”
He added: “The most common reason for staff leaving is for more sociable hours, which as a seven-day-a-week business operating from 4.30am until after midnight, is something we can’t compete with while also moving away from public facing jobs where the stresses are less immediate.
“Our Arbroath depot, responsible for operating the X7 service, is currently 25 drivers short. This equates to 17 per cent of the workforce.
“I appreciate that the current situation is extremely frustrating to those that rely on our services, as it is to us.
"The situation we face at present is not where we want to be and is one we are working hard to resolve. I would like to offer a guarantee that the situation will be resolved however I cannot commit to a timescale given matters are not wholly within our hands. ”
Tess White MSP said: “It’s deeply concerning to hear of the driver shortages Stagecoach is facing and the impact this is having on communities across the north-east.
“But these repeated cancellations are more than just numbers. Behind each of them are livelihoods being affected, from children and workers feeling unsafe walking home in the dark after a cancellation to the most vulnerable being left stranded in their homes with no access to lifeline services.
“This is why urgent action is needed to address the deepening crisis of driver shortages and I will be raising this in the Scottish Parliament.
“Stagecoach also needs to do more to improve the way it operates, both for drivers and customers, otherwise the X7 service will continue to face disruption which would be dreadful for our communities as winter approaches.”