The leader of the DUP has accused Sinn Féin of "pushing a radical all-Ireland agenda" during a speech to the party executive.
Jeffrey Donaldson said Mary-Lou McDonald and Michelle O'Neill should "stop obsessing" about a border poll.
He made the comments to the party executive and Assembly candidates on Saturday.
The DUP held a meeting to ratify their Assembly candidates for the election in May.
“There are those who like to tell us it doesn’t matter who wins this election. But they are wrong,” Mr Donaldson said.
"Current polls suggest there could be a Sinn Féin Taoiseach in the Republic of Ireland and a Sinn Féin First Minister of Northern Ireland after the next round of elections.
"Anyone who thinks the prospect of Michelle O'Neill and Mary-Lou McDonald touring around London, Brussels and Washington pushing a radical all-Ireland agenda will be good for the union, or help bring stability in Northern Ireland, is living in a fool's paradise.
“Just look at this week. Whilst all of Washington and New York were hailing their Irish ancestry and focused on Northern Ireland, Sinn Féin were not promoting Londonderry as a place to invest, they were taking out half-page adverts in the New York Times and Washington Post claiming now was the time for a border poll.
"Ladies and gentlemen, I have a message for Mary-Lou and Michelle O'Neill and Nicola Sturgeon. Stop obsessing about a border poll and focus on what matters to people.
"Focus on fixing our NHS, keeping our schools world-class, growing our economy, helping working families with cost of living and removing the shadow of the protocol from our politics.
“That is why this election is so important.
“That is why the DUP is focused on winning the election. That is why unionism must stand behind the DUP on May 5th.”
Mr Donaldson also revealed the party’s slogan for the upcoming Assembly election as “Moving Forward Together”.
Mr Donaldson said each voter would be faced with a “stark choice”.
“Between a positive vision for Northern Ireland – focused on the issues that really matter – or one centred on the chaos and division of Sinn Féin’s border poll plans,” he added.
“History has proven that this party’s success is Northern Ireland’s success.
“When this party is strong, unionism is strong.
“So, in the days to come, let us collectively rise to the challenge.
“Let’s not be afraid to make our case on the doorsteps and let’s seize the opportunity at this election to move forward together and ensure Northern Ireland moves in the right direction.”
Paul Givan resigned earlier this year as first minister as part of the DUP protest against the Northern Ireland Protocol, a move which also removed deputy first minister Michelle O'Neill from the joint office. – PA