The National Bus and Rail Union (NBRU) has called for a dedicated transport forum to deal with, what it describes as, long-running anti-social behaviour on a Limerick city bus route.
Bus Éireann has reduced services on the 303 route, between Southill and Moyross, after separate incidents in recent days.
The company said a driver was confronted by a number of youths while on duty at Carew Park last Sunday.
It says they boarded the vehicle and confronted the driver, before "exiting the bus and subsequently impeding the progress of the service".
Two days earlier, another driver sustained minor injuries, after she was shot with an air gun on the 303 bus in the O'Malley Park area.
Services from O'Malley Park and Carew Park have now been suspended.
NBRU spokesperson, Stephen Nugent, said that a driver on the 303 service was told that he would be shot by a group of youths last Sunday.
He said the vehicle was subsequently surrounded and struck repeatedly, by another group of youths, when it reached its final destination.
While the driver was not harmed, he was said to be shook by the incident.
Mr Nugent said the union could not have members working when their lives were being put at risk.
He said the actions of a small minority were having a huge impact on the service that many more people depended on.
The NBRU has called for a security presence on the buses between 5pm and midnight.
Mr Nugent said all stakeholders needed to take part in a forum to resolve the ongoing threats to his members.
He asked Bus Éireann, the National Transport Authority and local politicians to work with the NBRU and community groups to ensure services could run as normal.
Bus Éireann said it is keeping the situation under review and that the service in question will only run from Childers Road to Janesboro until further notice.
It has apologised for the inconvenience to customers as a result of the measures.
The service usually runs between Kilmallock Road and Pineview, through the city centre, with 60 scheduled runs, in both directions, each weekday.
The bus operator says it is assisting a garda investigation into both incidents and has made CCTV footage available to investigating officers.
