Leo Varadkar must come up with a plan B to resolve the political impasse in the north, Sinn Féin has warned.
The party's president Mary-Lou McDonald said her party will go into negotiations next week "with every ounce of energy that we can" but she remains "realistic" that talks may not break the deadlock to restore the Assembly.
She has also raised concerns around the timing of the latest Northern Ireland talks citing Brexit and upcoming elections as significant challenges to finding a resolution.
"I think it's a challenging time. Obviously, there are elections north and south and the issue of Brexit is ever with us so there is no doubt that there is awareness across politics that these are challenging times. But at the same time we cannot simply stand still so there is a need for action," said Ms McDonald.
"We will enter these talks with every ounce of energy that we can, that we will give it our full attention.
I want it to work. I want these talks to work but if they don't, well, the Governments having convened the talks need to have a plan B and they need to be clear that if the DUP persists in failing to answer these questions, then the co-guarantors of the agreements have to intervene.
Senior Sinn Féin sources have indicated that the party would be willing to let Westminster take power and legislate for marriage equality if talks break down.
However, Ms McDonald denied Sinn Féin and the other parties have been "bounced" into these latest talks by Taoiseach Leo Varadkar and UK Prime Minister Theresa May.
"It wouldn't be an acceptable scenario for the Government having initiated these talks, to simply shrug their shoulders and walk away. The days of disengagement, the days of tolerating inequality are over.
"I think society needs a win in this, I think the Governments in calling these talks have raised the stakes, they have certainly raised expectations not just that politicians will talk to each other but that politicians will land on answers and resolution. The stakes are raised in people's expectation that rights to marriage equality, to language rights, to the truth recovery processes, will finally be met."