The State Government has called for Huon MLC Paul Harriss to immediately resign from the upper house after announcing he would run as a Liberal candidate for the lower house in the March election.
Mr Harriss will stand in the southern electorate of Franklin in a move likely to make it more difficult for Labor to retain two seats.
That would leave Premier Lara Giddings and senior minister David O'Byrne to fight it out for one Labor seat.
Attorney General Brian Wightman confirmed the two would run in the seat.
Mr Wightman said it was farcical and arrogant for Mr Harriss to remain in the Legislative Council as an independent voting on critical pieces of legislation while he intends to be a Liberal candidate.
Greens Leader Nick McKim described Mr Harriss as having always been a ''closet Liberal'' and expected he would be the next Forestry Minister if successful at the election.