Sinn Féin has accused the DUP of betraying the interests of the North by agreeing to support Theresa May's minority government.
The republican party's leader at Stormont, Michelle O'Neill, predicted the confidence and supply deal between the Tories and the DUP would "end in tears".
Highlighting Conservative austerity cuts and its stance on Brexit, Mrs O'Neill (pictured) claimed the DUP link-up with Mrs May would spell bad news for the North, where a majority voted for Remain.
"It is no surprise that the DUP has agreed to prop up the pro-Brexit and pro-austerity Tory government of Theresa May," she said.
"They have once again betrayed the interests of the people of the north by supporting a Tory party which has cut funding to our public services year on year to the tune of hundreds of millions of pounds.
"Experience shows us that unionists have minimal influence on any British government.
"They have achieved little propping up Tory governments in the past and put their own interests before those of the people.
"This new arrangement between the DUP and the Tories will be transitory and will end in tears.
"But it will be the people of the north who will have to pay the price for the DUP's support for Brexit and for cuts."
Mrs O'Neill claimed the Conservatives had an "increasingly partisan approach" to the North and called on the Irish government to "stand up for the rights of all citizens in the north".
She repeated her call for the North to secure special designated EU status when the rest of the UK leaves the EU.
Developments at Westminster have placed a cloud of uncertainty over scheduled talks to restore powersharing at Stormont.
With the North having been without a devolved administration for three months as a result of a deep rift between the DUP and Sinn Féin, negotiations to re-establish the institutions are due to resume on Monday.
But many believe the prospects of a deal between the main two parties have receded even further now the DUP has aligned with the Conservatives, a party Sinn Féin is so vociferously opposed to.
Mrs O'Neill said: "Sinn Féin's focus remains on entering talks to re-establish an Executive which delivers for all on the basis of equality, respect and integrity and this requires the full implementation of agreements on rights and legacy."