Gilder services to Colin Connect in west Belfast have had to be withdrawn after windows were smashed on the vehicles in two separate attacks.
According to Unite, the union that represents drivers, one incident saw up to 70 youths involved in attacking a Glider at Lagmore after being put off for not paying.
A young female passenger is said to have narrowly escaped injury in another incident, when a window beside her was broken, but did not give way.
Michael Dornan, chair of the Metro and Glider drivers’ Unite union branch, said: “These are only the latest in a series of attacks on Glider services.
“The CRPOs, members of our union, who inspect tickets have been subjected to routine abuse for months now – many report being consistently spat at and attacked verbally by youths in anti-social behaviour incidents throughout the west Belfast route.
“Now the drivers are feeling the same pressure.”
Following the attacks, the Gilder bound for the Colin Connect terminus turned at the Michael Ferguson roundabout instead.
Davy Thompson, from Unite, added: “These attacks threaten life and limb – the responsibility for this outcome lies entirely at the feet of those who attacked the vehicles.”
On Tuesday, Translink confirmed that services were running normally again.
A spokesperson said: “We condemn attacks on our services in the strongest possible terms - thankfully, this is not a common occurrence.
“Following on from a very productive meeting this morning with Translink, Unite, elected representatives, PSNI, youth providers and Colin Safer Neighbourhood teams, a set of measures have been agreed to safeguard services to the community this evening and for the rest of the week.”