Philip McGuigan was urged to apologise last night after criticising Wrightbus of Ballymena.
DUP MLA Ian Paisley Jnr said that Mr McGuigan's "inaccurate comments" had put in jeopardy a multi-million pound contract that Wrightbus has just secured from the United States.
Mr Paisley said that employment figures from Wrightbus proved that Mr McGuigan's claims "don't add up".
He said: "The facts are completely different from the picture portrayed by the Sinn Feiner, whose real interest is to close down one of the largest employers in the country because it has a Protestant workforce and is owned by a prominent unionist.
"On Friday, I met with the industrialist William Wright and discussed the employment situation.
"The facts are as follows: From 2004 to 2006, the Protestant workforce has declined from 93.2 per cent to 81.7 per cent.
"That's a 10 per cent decline in the Protestant employees.
"During the same period, the Roman Catholic workforce has increased from 4.6 per cent to 14 per cent.
"The population of Ballymena roughly breaks down 80 per cent Protestant and 20 per cent Catholic, thus making the employment record of the company in line with local population requirements.
"Charges of discrimination simply just don't add up."
Mr Paisley accused Sinn Fein of trying to undermine Wrightbus.
"The company has never been charged with any discriminatory practice and has an excellent industrial relations record," he said.
"What have been most infuriating have been the unwarranted and unsubstantiated comments by an MLA who, the sooner is out of a job himself, the better.
"Such remarks by Philip McGuigan can only be designed to destroy employment opportunities for all in the locality.
"It is incredible that an elected representative would want to undermine a successful company because of his jaundiced view of the owner.
"It is now up to McGuigan to apologise for his comments and withdraw them and attempt to repair the damage he has done, not only here but also in America."