A member of Fianna Fáil's negotiating team in the government formation talks says climate targets have already been agreed.
Thomas Byrne told Newstalk Breakfast: "Already the two leaders had said that an average 7% reduction in emissions is what has been agreed between the two large parties.
"So this isn't a case of The Greens demanding something and not getting it - it's already been agreed to.
"I think what's happening at the moment is we're just trying to work out exactly the mechanics of doing that".
He said any deal 'needs to' be done by Friday or Saturday.
"I think there's a willingness on all sides to get a deal done, that's what I'd see.
"The urgency of doing it be Friday - it certainly will drift beyond tomorrow, I think - but the urgency is that our party, and indeed the other two parties, have to put this to their members.
"And with an effective deadline of the 29th or 30th of June, we do need that time to turn around a postal vote by members in terms of getting documents printed, in terms of posting out ballot papers and documents and getting the stuff back, and counting it.
"So that's a practical deadline that certainly we have, but I think the other two parties have that too.
"I think there's a genuine willingness to get a deal over the line in our party".
The talks continue on Wednesday after no agreement was reached on climate targets on Tuesday.
It looks as though it may be the weekend before any deal is reached.
Tuesday was seen as a crucial day to reach an agreement on how to achieve a 7% annual reduction in carbon emissions, and while some progress was made no agreement was reached.
There is frustration on all sides that the issue is still outstanding.
Some in The Green Party believe the two larger parties are trying to commit to a lower target by seeking an average reduction over the next 10 years - rather than a specific annual 7% commitment.
While sources in Fine Gael and Fianna Fáil are frustrated at what they see as a lack of workable ideas from The Greens.
It had been hoped a programme for government could be signed off on Thursday, but that now looks optimistic.
However, the Dáil's Business Committee has agreed to cancel Thursday week's planned Dáil sitting to allow the three parties involved to focus on government talks.
They hope by that stage to be selling their agreement to party memberships - but they have to get one in place first.
Reporting by Sean Defoe and Jack Quann