The future of Wrightbus is hanging “in the balance”, DUP MP Ian Paisley has said.
The Ballymena business was placed into administration and put up for sale in September.
English industrialist Jo Bamford, son of JCB chairman Lord Bamford, is understood to have bid for the company, but the ownership of the Wrightbus factory, at Galgorm, remains a barrier to an overall resolution.
Mr Paisley said it was “a good offer”.
The Unite union said the deadline to resolve the current impasse over site ownership was now 10:00 BST on Thursday.
“Today is decision day,” Mr Paisley told the BBC’s Good Morning Ulster programme.
“The administrator expects an answer today and if the answer is that we cannot get the deal consummated, in terms of the land sale deal, then I’m afraid the worst of all situations prevails and we’re left with liquidation of assets of the company.
“It’s either the continuation of building the best buses produced in the world or it’s the end of bus building in Ballymena.”
The Wrightbus premises are owned separately from the manufacturing business and held in a company called Whirlwind Property Two, which is not part of the Wrights group and is therefore not under the control of the administrator.
The property company is controlled by Jeff Wright, the former owner of Wrightbus.
Mr Paisley said that Mr Banford “is only one preferred and exclusive bidder” but that the land remained the final hurdle to the deal, and Mr Bamford was not going to invest tens of millions of pounds if he did not control the asset.
He said Mr Banford told him on Tuesday that jobs would be created within two weeks, if a deal is made.
“The Wright family have made a mammoth contribution to Northern Ireland over three generations and this maintains that rich history,” said Mr Paisley.
“Everyone needs to put their shoulder to the line and get this deal over the line.”