Sandwell Council has said it may have to make up to 700 job cuts over the next three years as it seeks to cut its spending by £67m.
The GMB Union has said it fears it may be as many as 1,000 jobs.
The council has agreed a shake-up that will cut the number of top managers by half, saving more than £1m a year.
Council leader Darren Cooper said there would be a new system of area directors and a senior management board.
The top tier of management at Sandwell Borough Council has been cut from 26 to 13.
Mr Cooper said there would be a new system of area directors and a senior management board.
He said he had always pledged that any cuts that had to be made would come from the top.
The Labour-controlled authority currently has a chief executive, four executive directors, five directors and 16 heads of service.
This set-up will be replaced with a chief executive, two corporate directors and 10 directors.
A GMB spokesman said the union had been informed of up to 700 job cuts but said he feared the number could ultimately be higher.
He said the union would meet community groups to see if it could help mitigate the cost of the job cuts and talk to its own members to ask them what they want the GMB to do.