The Ulster Unionist Party leader is expected to rule out “begging” for concessions in exchange for supporting any coalition government after the general election.
Mike Nesbitt will say he has good relations with the Conservatives and Labour during his party’s manifesto launch on Friday.
The DUP is seeking extra money for Northern Ireland and changes to welfare proposals in exchange for supporting the next government during a hung parliament.
Mr Nesbitt will say: “We will do our best for the people of Northern Ireland, but our values are not an auction item.
“We will not take short-term advantage if it means long-term damage to the Union and to our children, and grandchildren and future generations.
“So, no begging bowl approach from us, come May 8.”
The UUP had no members of the last parliament.
It has agreed a pact with the DUP which will see it standing aside in East Belfast and North Belfast in exchange for support for its own “unionist unity” candidates in Newry and Armagh and Fermanagh and South Tyrone.
Mr Nesbitt will outline his party’s manifesto for the next parliament at an event in Portadown, Co Armagh.
He is likely to say: “If we are returning to the green benches we will have an important role to play in the next Westminster mandate.
“Who will we support as the next Government?
“We have good relations with both of the parties who have the only realistic hope of occupying 10 Downing Street on May 8.
“We will see what they have to say.”
He will acknowledge uncertain times for the Union following Scotland’s vote on independence and moves towards greater devolution.
“Like other nations and regions, we want more power, not least the power to set our own rate of corporation tax,” he will say.
“But we do not want to see the break-up of the Union.
“If we are returned to the House of Commons, Ulster Unionists will do what we have done for over 100 years.
“We will contribute: politically, economically, militarily, culturally, socially.
“The Union is not a one-way street.
“The Union is not just about the money.”