Sinn Féin has called on the SDLP to stand aside in two constituencies in the North to maximise the "anti-Brexit vote", but has not offered a reciprocal move.
Michelle O'Neill, the party's Stormont leader, urged SDLP leader Colum Eastwood to "do the right thing" and not field candidates in Fermanagh and South Tyrone and North Belfast.
In both constituencies, Sinn Féin is attempting to displace a sitting unionist - DUP deputy leader Nigel Dodds in Belfast and former Ulster Unionist leader Tom Elliott in Fermanagh.
While Mrs O'Neill called on Mr Eastwood to withdraw from those two races, she did not offer to do the same in constituencies where the SDLP is potentially better placed to win, insisting Sinn Féin would stand in all 18 constituencies.
"If the SDLP believe in that anti-Brexit position that they consistently said in their public narrative then they should do the right thing," she said.
After making the announcement at the party's offices in west Belfast, Mrs O'Neill faced questions on what the SDLP would gain from such an offer.
She responded: "They get the maximum number of MPs returned which are going to be anti-Brexit, which is their position."
Last month, the SDLP, Sinn Féin and the Green Party held talks on a potential anti-Brexit electoral alliance but those discussions faltered when the Greens withdrew.
At the time, Mr Eastwood insisted he would not contemplate a two-party deal with Sinn Féin, insisting that any link-up would have to be cross-community in make-up.
Mrs O'Neill denied she was now offering a "sectarian pact".
"This is not about pacts and it is certainly not about a sectarian pact, it's about maximising the number of MPs who are returned who have adopted the position that is anti-Brexit, which is clearly what the wishes of the people of the north here voted last June," she said.