Irish Rail has said that passengers cannot use their own reusable cups on Intercity services.
This is due to health and safety concerns as trains could move suddenly and cause injury.
Irish Rail is also considering introducing its own version which can be bought for repeated use.
A company spokesperson said trains can travel at 70 miles per hour and could jolt suddenly.
Jane Cregan they were not operating in a coffee shop environment so keep cups could not be accommodated.
She also said the varied size cup sizes and lids not being closed properly could also pose a risk to safety.
Ms Cregan said: "We understand that customers want to be more sustainable but safety has to be our number one priority."
Meanwhile, the Government is proposing to introduce a charge on non-reusable cups to tackle plastic waste.
This could add up to 25 cent per cup.