Sinn Fein leader Mary Lou McDonald has said she will raise the issue of a border poll with Boris Johnson in the coming days.
Addressing party members at an event in the Mac Theatre in Belfast, Ms McDonald accused the new Prime Minister of trying to "bully" the European Union and the Irish Government over Brexit.
"What everyone thinks of Boris Johnson and his apparent desire to be the next Winston Churchill, it is a truism of the long tortured relationship between our two islands that every British Prime Minister has approached the issue of Ireland on the basis of British self-interest," she said.
She added that his demand for a new withdrawal agreement and to scrap the backstop would not be accepted.
"The EU said no, the withdrawal agreement is not up for renegotiation, so the British Government cannot and will not intimidate the Irish Government or the people who voted to remain," she said.
"Those days are long gone. The backstop is the bare minimum required to safeguard Irish interests."
Ms McDonald said Mr Johnson was trying "to set the clock back" by threatening to reintroduce direct rule.
Regarding efforts to restore Stormont, she said the latest round of talks with the DUP had again "failed to reach agreement".
"The DUP focus is on protecting the union with Britain above else, regardless of the consequences for society, the economy and for our people," she said.
"They ignore the anti-Brexit vote of the northern electorate. Some DUP leaders see a hard border as the best way to maintain the union.
"A new partition of Ireland, this is folly. This contradicts the search for agreement and the restoration of the institutions."
Party members were told the aim was still to restore Stormont, but the British Government continue to "collude in the continuing denial of rights and they refuse to implement agreements on an Irish language act and dealing with the past."
With the prospect of a no-deal Brexit increasing, Ms McDonald pointed to a recent report from the Department for the Economy that said crashing out of the EU could risk 40,000 jobs in Northern Ireland.
"This is a huge number of job losses for a small region," she said.
"The DUP refuses to acknowledge what their Brexit will mean for our businesses, for our agri-food producers, our workers, our community sector if the British crash out of the EU with no deal."
Addressing the Irish Government, she said it was now "irresponsible" not to prepare for constitutional change, and called on the Taoiseach Leo Varadkar to appoint a dedicated government minister to plan for Irish unity.
She added that a forum on Irish unity should include unionist views, noting that figures such as Peter Robinson, Eileen Paisley, Mervyn Gibson and the actor James Nesbitt had already addressed the issue seriously.