The Dail will vote tonight on whether the National Maternity Hospital should be built on public land.
Green Party TD Neasa Hourigan says she plans to go against government and support the Sinn Fein motion.
Cabinet yesterday signed off on the relocation plan, which will see the hospital built on land not owned by the State.
Her fellow Green Party TD, Patrick Costello, has also voiced his opposition to the move, but has yet to indicate if he will also support the motion.
However he says he won't be resigning from the party over it.
"I don't necessarily see that as the obvious next step. I've listened to a lot of constituents, I've made representations on behalf of my constituents to my cabinet colleagues, and they're the ones who hold the power on this issue.
"I alone don't make up the government's majority, they're going to go on with or without me.
"The reality is that I'm in a better place to represent my constituents by staying inside for the moment."
