A union leader has warned that a strike by council workers in Southampton could cost the authority millions of pounds.
Workers, including traffic wardens and toll collectors, are walking out over proposed pay cuts and a pay freeze.
Unison deputy general secretary Keith Sonnett said the strike would continue until the council began "treating workers fairly".
It comes as Unison announced it will ballot 10,000 of its members at Tory-led Birmingham City Council.
The union said the move was in response to plans to cut £300m from the city budget by 2015, and axe more than 7,000 jobs by 2015 - over a third of the workforce.
Mark New, Unison's regional organiser, said: "Birmingham council is cutting back too hard and too fast.
"The cuts will devastate whole communities and the local economy, as well as the lives of council workers and their families."
In Southampton, deputy leader of the Conservative-controlled authority, Jeremy Moulton, blamed the unions for making the situation worse.
Mr Sonnett, who addressed a workers' rally in the city earlier, said: "Southampton council bosses must start listening to staff, or see millions in revenue wasted as the strike continues."
Mr Moulton said: "Less money means more pressure on jobs and services. By taking this action unions are directly affecting the very people they should be trying to protect."
Toll collectors on the city's Itchen Bridge are due to walk out for seven days from Monday in a move unions estimate will cost the council £250,000 over the coming weeks.
Parking wardens striking in Southampton have extended their walkout for a further seven days.
Up to 40 traffic wardens, maintenance engineers and bulk cash collectors went on strike on Tuesday over the proposed pay cuts.
It follows industrial action by refuse workers last week, who announced they will strike again on Saturday.
The unions said the workers faced a 4.5% wage cut, plus a three-year pay freeze and a loss of annual pay progression for two years.
In February, the council finalised £25m budget cuts and said all workers earning more than £17,500, which is 65% of staff, would have their pay cut by reducing working hours.
The council employs about 6,600 staff.