Dublin Bus services have been the target of almost 1,000 anti-social behaviour incidents in 2019.
Among the worst hit areas were Tallaght, Clondalkin, Neilstown Ballymun and Finglas.
The National Bus and Rail Union has said that "no other occupation" would tolerate the levels of anti-social behaviour in the workplace.
The Irish Times reports that the letter issued by general secretary Dermot O'Leary criticised a decision to not set up a dedicated transport police.
There were also 90 incidents of anti-social behaviour on Bus Eireann, with one driver seriously assaulted in Naas.
Mr O'Leary said that the people involved in such anti-social behaviour "were operating across public transport with impunity".
There has also been a 43% increase in anti-social behaviour on Irish Rail services over the last two years.
