Small and medium businesses should be excluded from collective bargaining agreements to which they are not signatories, the Democratic Alliance said on Wednesday.

"The DA will write to Small Business Development Minister Lindiwe Zulu requesting she advocate for the exclusion of small and medium business enterprises from collective bargaining agreements which they are not signatories to," DA MP Toby Chance said in statement.

This should be done through changes to the Labour Relations Amendment Act.

"This follows ongoing strike action within the metal and engineering sector [after] the signing of an agreement between major workers' union Numsa and major employers' association Seifsa.

"Sustained strike action within the sector comes as a result of continued haggling over wage disputes between Numsa and the smaller employers' association -- representing 3000 small and medium size businesses - the National Employers' Association of South Africa (Neasa)."

Chance said Neasa was currently not bound to the terms of the agreement between the National Union of Metalworkers of SA (Numsa) and the Steel and Engineering Industries Federation of Southern Africa (Seifsa), and had threatened to challenge it should the agreement be formally gazetted.

"Neasa maintains that its members cannot afford the 10 percent annual wage offer for three years agreed to by Seifsa and Numsa," he said.