NUM and Cosatu said on Tuesday they support the mass strike for better wages.
"The NUM support Numsa in their fight to close the apartheid wage gap, fighting for equity in the workplace, and demanding a living wage... It is important for the working class to continue fighting for better salaries and better working conditions," the NUM said in a statement.
Cosatu described Numsa's demands as reasonable and called on its affiliates to back the strike.
"We
agree with Numsa's determination that they are not going to be
intimidated by all those who represent the class interest of business
and big capital," Cosatu said in its statement.
Thousands of striking metal sector workers arrived at their industry's bargaining council in central Johannesburg to deliver a memorandum to officials from the Metal and Engineering Industries Bargaining Council.
Numsa members were protesting in Cape Town, George, Durban, Port Elizabeth, and East London.
One worker said that they are ready to strike indefinitely, like their counterparts in the platinum mining sector."We can go on for months like the mineworkers... this is for our welfare and that of our children, and future generations too," said one worker, Mapula Seale, 48, during the protest in Newtown.
Wearing a Numsa T-shirt and a red bandana, Seale said employers in the country did not act until there was a full-blown strike.
"Workers in Marikana showed us that patience and resilience is needed to achieve what one is fighting for," she said, referring to platinum mineworkers in the North West.
Seale, a mother of three, works at a company in the engineering sector that supplies car ignition systems.
She was accompanied by Lorraine Mkhize, whose employer, a steel manufacturing company, supplies Eskom and Telkom with steel.
She said she took home about R3 800 every month.
"I am drowning as I try to pay school fees and put food on the table. We want the 12%, and we are going nowhere until we get it," Mkhize said.
Numsa, the majority union in the sector, wants a 12% salary increase,
the scrapping of labour brokers, and a one-year bargaining agreement.
A deadlock in negotiations led to a strike notice from Numsa, as well as the Chemical, Energy, Paper, Printing, Wood, and Allied Workers' Union, and the General Industries Workers' Union of SA.
Employers have tabled a three-year wage settlement offer of between 7-8% for different levels of workers in the first year, and CPI-linked increases for 2015 and 2016.