The Taoiseach says he can't promise Ireland's corporate tax rate will remain at 12.5%.
Over 130 countries in the O-E-C-D have signed an agreement to have a worldwide rate of at least 15%.
The deal's due to be finalised in about six weeks' time, and Ireland has so far refused to sign up.
But speaking to Bloomberg on a visit to the US, Micheál Martin didn't rule out joining the global agreement.
"We're part of the OECD process, we've engaged with that process constructively, and have been since 2013.
"We haven't joined the consensus yet, we've been broadly supportive of the process, but we haven't signed up to the consensus yet because of some aspects of it which we believe do not give certainty of continuity."
