* Council workers to strike from Monday
* Chemical union says new offer still below its demand
* Telkom, rail workers may also protest
* Increases pressure on govt after service protests
(Recasts with other strikes, protests)
By Gordon Bell
JOHANNESBURG, July 24 (Reuters) - South African council workers are to strike over wages from Monday, unions said, in a move that could hit public services when thousands of people have been protesting over poor housing and unemployment.
A chemical sector union was also on Friday considering an improved pay offer to end a separate strike, while transport workers at the national rail operator are to decide on Monday whether to take industrial action.
Africa's biggest economy has been hit by a wave of strikes over wages during the salary negotiations season, as well as protests about poor services, increasing pressure on new President Jacob Zuma who rose to power with union backing.
The demonstrations have so far had little impact on markets but analysts have warned that this could change if strike action continues for long and became more widespread.
Zuma, facing added pressure from unrest in townships, said police will move swiftly to crack down on rioters after violent protests erupted this week over poor services and jobs.
The South African Municipal Workers Union (SAMWU) and Independent Municipal and Allied Trade Union (IMATU), which say say they represent 150,000 council workers, resolved to strike, after rejecting a proposal of an 11.5 percent increase.
"We can confirm the strike is going ahead on Monday. Both unions have a mandate to strike. We will only rescind that strike call when there is any offer from management," SAMWU spokesman Stephen Faulkner said.
He said union officials would meet Cooperative Governance Minister Sicelo Shiceka later in the day.
"We are hopeful there will be some outcome and we can then put that to our members early next week (but) the strike is definitely going ahead."
A strike could see among others, refuse and transportation workers, licensing officers and city police stay at home.
The country's powerful unions helped propel Zuma to power in an April election on a pro-poor platform. But instead of an expected cosy relationship, they are using their most powerful weapon -- strikes -- to press their agenda.
A chemical sector strike, which began on Monday, may stretch into next week despite an improved offer from employers.
The Chemical, Energy, Paper, Printing, Wood and Allied Workers Union (CEPPWAWU) said employers had raised their wage hike offer but to a level still below the union's demand of at least a 10 percent rise.
Its deputy general secretary Thabane Mdlalose said the strike would continue while the union consulted its members.
"We don't think we will get an agreement now, but we need to take it to our members and have them decide," he told Reuters.
The union expects to meet with employers on Saturday or Sunday, he said, adding that talks continued with employers in the pharmaceuticals and paper sectors, with offers unchanged.
African Oxygen (Afrox), (AFXJ.J) Africa's biggest gas and welding firm, said it was monitoring the impact of the strike on its customers while it awaited the union's response.
"Priority has been given to medical facilities normally supplied from Afrox operations where personnel are on strike," said spokesman Simon Miller.
Affected companies also include South African petrochemicals group Sasol (SOLJ.J) and chemicals firm Omnia <OMNJ.J. Telecoms group Telkom (TKGJ.J) will also be impacted by a communications workers protest.
"We will give Telkom a 48-hour notice to strike on Monday," said Gallant Robert, general secretary for the Communications Workers Union.
Gold and coal unions are considering a pay offer. If they reject it stoppages will hit some of the world's biggest mines.
Workers in the coal sectors will announce on Tuesday whether they accept an improved offer from mining firms. (Reporting by Gordon Bell, Gugulakhe Lourie, Agnieszka Flak and Alison Raymond)