While the Sun-Times Media Group has received an offer for its purchase, before the sale may be finalised it must have the approval of the company's unions, which face significant contract concessions, the Chicago Tribune reported Thursday.

Union representatives are shocked at the cost reductions they are being asked to make, which is a prerequisite for the sale of the bankrupt U.S. publisher.

"This basically guts our contract. It's a terrible, terrible thing," Tom Thibeault, executive director of the Chicago Newspaper Guild, told the Tribune. "I do not anticipate our members supporting this."

The concessions as part of a new three-year contract, which includes a reduction of the severance pay out from 50 weeks of wages to just four, the right of management to transfer and reassign employees without consulting unions and the elimination of seniority rules when making staff reductions.

Staff fear making such concessions to allow the company to keep operating will then see them without a job, according to the Tribune.

A private investment group led by Chicago banker Jim Tyree was announced as a potential purchaser on Monday.