A large number of employees will be made redundant at Wrightbus later, it has been claimed.
The family-owned firm from Ballymena built London’s distinctive red double decker Routemaster buses when Boris Johnson was mayor of the capital.
Mr Paisley said unions were being briefed by managers on Wednesday morning.
He told the BBC: “Essentially, from this point the administrator has a week to find a buyer.”
Stormont Assembly member Jim Allister said it was devastating news and the heart had been ripped out of Ballymena.
“The rollercoaster ride of the last few weeks has added to the torment brought to the management and employees.
“For decades Wrightbus has been a constant and provider of thousands of jobs.
“Amidst the sadness of today I want to salute Sir William Wright for the vision and commitment which he brought in building up this company and providing good income for so many. He did not deserve this tragic outcome.
“However, Wrightbus has a great product. The combined efforts of us all must be to ensure that it does not become a fading memory but obtains a flourishing new beginning.”