Irish Rail has been forced to make schedule changes due to a number of drivers self-isolating.
The popular Sligo to Dublin route has seen some services cut, with seven trains now travelling each way daily.
The rush hour services that would typically depart around 4pm have been suspended. However the 5.10pm service from the capital remains in operation.
In addition to drivers needing to self-isolate, there has also inevitably been "significantly reduced" demand, in part due to the current Level Three restrictions as people are advised only to enter or leave the capital for essential reasons.
The Covid-19 pandemic also means there are less commuters, both for work and college, as businesses and universities move online.
An Irish Rail spokeswoman said: "We have a marginally reduced schedule of 7 trains each way daily, arising from ensuring service continuity due to varying levels of self-isolation amongst employees, and significantly reduced demand.
"This will be kept under review.
"Our priority is the safety of our customers and employees, and we will ensure as we have throughout COVID-19 that self-isolation amongst employees takes place in line with HSE guidelines."
