The DUP MP Ian Paisley has said the administration of Wrightbus is now an "inevitability".
The company is suffering from cashflow problems and has been seeking investment or a new owner.
Mr Paisley said he understood administration would commence on Wednesday.
The firm is best known for building the New Routemaster, known as the 'Boris Bus.'
"Essentially from this point the administrator has a week to find a buyer," Mr Paisley said.
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Unions at Wrightbus are due to be briefed by managers on Wednesday morning.
Mr Paisley said employees would be told what the process would mean for them.
Talks with two potential buyers failed to reach a conclusion last week. The company is not commenting.
Latest accounts show that the Wrightbus group lost £1.7m on a turnover of £227m in 2017.
But its financial situation has deteriorated since then.
It made two rounds of redundancies last year with 95 jobs going in February and June, which it said reflected continued low levels of demand for new buses in the UK market.
The UK has traditionally been Wrightbus's biggest market but it has been contracting for over two years.
Figures from the Society of Motor Manufacturers and Traders (SMMT) show that in the second quarter of this year new bus and coach registrations are down 30% compared to the same period last year.
That marks the tenth quarter in a row that new registrations have declined.
Mr Paisley said it was a "terrible time for the employees and their families."
The North Antrim MP added: "All 1500 of them deserve our support. The supply chain workers also face troubling times.
"The company has been working very hard to conclude a sale but difficult decisions need to be made and time has run out."
He said he had met unions, management and employees on Tuesday.
Mr Paisley added that he would meet the prime minister and the secretary of state to discuss the next part of the process on Wednesday.