South African firefighters who went on strike in Canada were 'ruthlessly' exploited, the National Union of Metalworkers of SA (Numsa) said on Thursday.

"[Numsa] warmly congratulates the 301 fire-fighters who protested at the way they were being ruthlessly exploited while they were courageously fighting fires in Alberta, Canada," said the union's acting spokesperson, Patrick Craven, in a statement.

The firefighters, who arrived in Canada on May 30, returned home this week. They had gone to assist with wildfire suppression, as part of a resource sharing agreement with Canadian firefighting agencies.

The team, whose members are drawn from marginalised communities, has been trained in fire prevention and suppression, first aid, carpentry and health and safety through the Working on Fire (WoF) programme which is part of the government's Expanded Public Works Programme.

Craven had harsh words for WoF, calling it "a cheap-labour scheme to exploit workers who ought to be properly employed in the public service and paid a living wage".

Previously, WoF chairperson Johan Heine denied claims that the initiative was skimming from the $170 a day the Canadians were paying, and only paying firefighters $50 a day.

He said the firefighters were earning R720 a day while in Canada, "and suddenly they are demanding R3 000 a day".

They earned their normal salary - between R100 to R650 a day depending on their seniority, plus a R70 a day away from base allowance, plus a R50 a day out of country bonus, Heine said.

However, Craven said that the firefighters and others on such government schemes were "being ripped off and super-exploited".

This week, Environmental Affairs Minister Edna Molewa asked South Africans not to condemn the firefighters for their actions, saying that the group was no longer needed because of heavy rains in the affected region of Canada.

Molewa also said she had sent a mediator from WoF to Canada to assist in resolving the dispute. An internal inquiry will take place.