About 4,000 staff are facing a pay cut

About 4,000 staff are to have their pay reduced, although the council said about 45% of its 41,000 workers would receive a "considerable increase".

A Unison spokesman said ballot papers were being sent out to staff and a rally was planned later in the month.

Council chiefs said they were legally obliged to carry out the plans.

Some staff members have said they could lose up to �6,000-a-year if the proposals are carried out.

The council said it was among authorities across England which had been asked by the government to bring the pay schemes in line with equal pay legislation.

Hundreds of council staff protested about the plans outside Birmingham's Council House as part of a rally in November.