The SDLP has ruled out co-operation with Sinn Fein while a top unionist called for greater efforts to combat republican political ambitions.
After prominent SDLP member Declan O'Loan caused a storm by effectively proposing a merger with Sinn Fein, his leader Margaret Ritchie has again ruled out such a move.
This came as Ulster Unionist Danny Kennedy told an Orange Order event that his party should co-operate with the DUP to halt Sinn Fein's growth.
Mr Kennedy said: "Unionism must challenge the Sinn Fein agenda and to do this effectively it must stand together instead of pursuing the negative and ultimately unproductive politics of division. Unionist disunity has been Sinn Fein's opportunity. Sinn Fein has successively inflicted serious damage on both main unionist parties and on their leaderships.
"It is time for unionism to come together and work together." Calls for unionist unity have grown after Sinn Fein topped the poll in both the European and general elections.
If Sinn Fein emerges as the largest party in the Assembly election, it could see the party score a symbolic victory, with Martin McGuinness possibly moving from the deputy First Minister's role into that of the First Minister.
Unionists have considered how to avoid the development and Mr Kennedy has repeated calls for unionist co-operation which stopped short of a full merger between the UUP and DUP.
He said if the Conservatives could work closely with the Liberal Democrats to form a government at Westminster, the unionist parties could also work together at Stormont. He added: "This model - the concept of a coalition of unionist parties - may be a more productive route for us to follow in that it allows the parties to retain their separate, distinct and historic identities while working together for the good of unionism and the union."
On Friday, SDLP leader Margaret Ritchie announced that she had lifted Declan O'Loan's suspension from party ranks over his nationalist unity call.
But in a weekend speech to party members, she ruled out any co-operation with republicans. "I can see no credible argument for closer ties with Sinn Fein," she said. "A closer tie with Sinn Fein leading to a single nationalist party is a step beyond the pale for me."