The Democratic Alliance's (DA's) proposed bill to hold unions responsible for violence during strikes will be shot down, the South African Communist Party (SACP) and the Congress of South African Trade Unions (Cosatu) said.

"We want to say to the DA, forget about what you are trying to do," said SACP general secretary Blade Nzimande.

He was speaking at the South African Democratic Teachers' Union congress in Boksburg, which ends on Friday.

"That is a sure route to destroy the trade union movement in South Africa," he told Sadtu members.

Nzimande said that people could be "planted" during the strikes to cause a "distraction" and this could harm the union's financial viability if it were sued.

Also speaking at the congress Cosatu general secretary Zwelinzima Vavi said the bill was an attempt to "weaken" and put the working class on the "back foot".

"That so-called bill is not going to see its way even to Parliament... we can't allow that very, very corrupted logic," he said, adding that he was not surprised that it came from the DA.

DA MP Ian Ollis this week told reporters that the bill sought to amend the Labour Relations Act of 1995 and make unions partly responsible for illegal actions during strikes.

It proposed that unions took steps to prevent, repair or remedy injury to persons and damage to property caused by strikes.

Also, it proposed that unions be held responsible for damage, loss or injury as a result of strike action.

Ollis said union bosses would have no problem with the bill if they agreed that strikes ought to be orderly and peaceful.