A council is to appeal a finding that it acted illegally by issuing dismissal notices to 345 white-collar staff without consultation.
Middlesbrough borough council gave out dismissal notices the day after councillors approved the compulsory redundancies.
Staff included architects and planners employed by the authority's economic development and transportation department.
An employment tribunal found in favour of unions representing more than 100 of the employees.
Now, the authority is waiting for a date to be fixed for an appeal hearing.
The tribunal found the unions' complaint that the council did not consult was "well-founded".
The council denied failing to follow the law on consultation.
The judgement said the council contravened the Trade Union and Labour Relations Act. Under this, employers proposing to dismiss more than 20 employees within 90 days must consult the staff or their representatives.
The judgement said, "The tribunal is satisfied that the events described demonstrate that negotiation and consultation were about precise numbers, selection criteria and practical arrangements rather than about the principle of redundancy itself."
In the final event,104 employees were made redundant.
Counsel for Middlesbrough, which employs about 8,000 staff, argued that employers are not acting illegally as long as consultation has started by the time dismissal notices are issued.
Mike Brider, of the Transport and General Workers Union, said he expects the case to cost the council up to £250,000.
A council spokesman said costs are likely to be substantial.