An inquiry has been called for into why a Liberal Democrat council signed a contract for a casino on the day it lost power in a landslide election.
The deal will bring a £13m face-lift for the grade II listed Pavilion
Bournemouth Borough Council signed the contract with Trevor Osborne Property Group on 3 May as voting was under way.
On coming into power, the new Tory administration vowed to stop the casino plan, only to find out later that the deal had already been signed.
Tory MP Tobias Ellwood has demanded an inquiry into the "shocking move".
It could cost the newly-elected Tory council as much as £6m to get out of the contract if it decides to halt the controversial town centre casino scheme.
In an open letter to the council, Mr Ellwood, the MP for Bournemouth East, said it was "widely expected" that the Lib Dems might lose power, which made the timing of the multi-million pound contract all the more "worrying".
The Conservatives won control of Bournemouth Borough Council in a landslide victory from the Liberal Democrats last week, gaining 23 seats to make a total of 41, while the Lib Dems dropped from 30 seats to seven.
Local Tory councillors, who used the casino issue in their election campaign, insist they were always opposed to the casino plans.
But former Lib Dem deputy leader of the council Adrian Fudge called the row "pure electioneering and political posturing" and said Tory councillors in opposition had not formally objected to the casino over the past three years.
He added: "Why didn't they do their job as opposition and move against this at a much earlier date?"
The contract was signed on election day to meet the deadline for the casino to obtain a licence, he said.
Mr Fudge said the casino was only 6% of the scheme, which would bring up to £60m private investment to the Dorset town and include restaurants, a family attraction, a tourist information centre and a £13m face-lift for the grade II listed Pavilion.