The Unite union has said it fears that Stormont budget cuts are having a 'devastating impact' on public safety at Translink.
The union has released photographs of a tyre on a vehicle that it says was judged by Translink's engineering management to be safe to drive.
Unite regional officer, Davy McMurray, claims the driver was subsequently suspended for refusing to drive the vehicle.
Mr McMurray said: "The vehicle’s driver was suspended without pay after refusing to take it on the road although she has been reinstated following Unite representations on the issue to senior management.
"Our fear is that this is not an isolated incident and that management are intent on turning a blind eye to safety concerns in order to avoid incurring costs and to live within the reduced budget provided by the Stormont Executive.
"While we recognise the insurmountable challenges posed by the severity of austerity cuts, our drivers and engineers will not be silent when passenger safety is compromised."
He added: "Our union is committed to defend public transport in Northern Ireland and whilst we continue to engage constructively to find genuine offsetting savings to safeguard frontline services and jobs, our members will not stand idly by when they have concerns over passenger safety."
A Translink statement said: "We are fully committed to ensuring we maintains [sic] our vehicles to the highest standards with the safety of passengers and staff paramount.
"We can confirm the vehicle was inspected by engineering staff and our tyre supplier who all confirmed that at no time was the vehicle operated in an unsafe condition. We have a robust regime of vehicle inspection and our procedures comply with the highest industry standards.
"We continue to engage with our staff and representative trade unions on all matters relating to safety."