Diane Dodds urged unionists to vote in next weeks election
If Sinn Fein topped the poll in the European election and two nationalists were elected it would be a "disaster for unionism", the DUP has warned
Launching its manifesto on Thursday, the party warned unionists against staying at home and not voting.
The DUP has come in first in every European election since 1979.
However this time they face the rebranded Conservatives and Unionists, and the former DUP candidate Traditional Unionist Jim Allister.
Diane Dodds is under pressure to match past performance.
Mrs Dodds told party supporters gathered in an activity centre in the Belvoir estate in south Belfast that she wanted to keep the DUP first and to assist a second unionist getting elected.
"Republicans are counting on unionists sitting at home or wasting their votes on candidates that cannot win.
"Sinn Fein's success," she argued in an implicit reference to the TUV's Jim Allister, "is dependent on vote splitting by a candidate that wants to destroy devolution. Let's not play into their hands."
The DUP manifesto stresses the benefits of devolution at Stormont, which it argues is delivering peace and stability.
It says the party will not sign up to devolving policing and justice until satisfactory financial and political arrangements are in place
On European issues, it opposes the adoption of the euro and what it calls the devastating consequences of the Common Fisheries Policy which sets quotas for local fishermen.
The party is asking its supporters to transfer to other unionists.
Although the DUP describes Jim Allister as "a lone maverick" who wants to plunge Northern Ireland back into crisis, the party leader Peter Robinson declined to advise his voters not to transfer to the Traditional Unionist leader.
Mr Robinson predicted that the electoral pact between the Ulster Unionists and the Conservatives "would end in tears".