One in seven contractors for Irish Rail failed a random drugs test in the past year.
The company's confirmed it's considering putting mandatory drug testing in place for all workers as a result.
The state company outsources certain jobs and functions for the railway network, like track maintenance.
Iarnrod Eireann also carries out spot checks on its full time staff (around 5% of the 3,700 workforce), but the one-in-seven rate relates to contractors.
Spokersperson Barry Kenny has told 98FM News the "figure is a concern and is significantly high enough for the company to look at taking the action they need to take."