Forcing Martin McGuinness out of office should be a top Traditional Unionist Voice priority at Westminster, its leader has claimed.
Jim Allister said legislation making the Sinn Fein chief Deputy First Minister in the Northern Ireland Assembly should be repealed.
The hardline unionist opposes power-sharing at Stormont with republicans and said a hung parliament could give unionists greater leverage.
"One of the most shameful events of the last parliament was when the unionist title deeds to the position of First Minister were surrendered," he said.
"The legislative change taking the post away from the biggest tradition in Northern Ireland, passed in November 2006, must be repealed."
The office of First Minister is legally an equal partnership between Democratic Unionist First Minister Peter Robinson and Deputy First Minister Mr McGuinness.
Mr Allister added: "I appreciate this will be difficult and embarrassing for the DUP, since they connived at achieving this monstrous change, because (First Minister) Peter Robinson thought it would create a 'clever device' to duress unionists into voting DUP.
"But the opportunity in a hung parliament to reverse this catastrophic mistake is more important than DUP embarrassment and, therefore, should be grasped."
He said imposing a Sinn Fein "First Minister" on a unionist was a "monstrous insult". "It must go and in a hung parliament we can get rid of it if every unionist MP makes it the price of any vote," he added.
Former barrister Mr Allister is running in North Antrim, the seat of former DUP leader the Rev Ian Paisley. He has built his campaign around opposition to power-sharing.