The National Union of Metalworkers of South Africa (Numsa) and the South African Cabin Crew Association (Sacca) said they had had constructive discussions with the government on ensuring the continued existence of troubled national carrier South African Airways (SAA) and fellow state-owned airline SA Express.

The unions have been critical of the practitioners appointed after the government placed financially-strapped SAA under business rescue last year, accusing them of a lack of commitment to reviving the airline.

In a joint statement released late on Tuesday, after SA Express (SAX) was placed under provisional liquidation, the unions accused the practitioners of putting undue pressure on employees to sign what they called hollow and conditional retrenchment agreements "tantamount to workers being forced to essentially relinquish their rights".

"This takes place in circumstances where there is an unequivocal commitment from government to do everything reasonably possible to save SAA in the interests of workers and the country as a whole," Numsa and Sacca said.

"Not only will workers voluntarily put themselves out of employment with no guarantee of any reasonable package, but signing will assist those who are intent on destroying SAA and strip its assets to the detriment of all South Africans."

The unions said they had spoken with public enterprises minister Pravin Gordhan about the provisional liquidation of SA Express -- which is operationally independent of SAA but incorporates its flights within a strategic alliance with the national carrier -- and were satisfied that the government was committed to finding a sustainable solution to the challenges facing the airline.

This musts happen before the first week of June when a decision will be made in court as to whether to place SA Express in final liquidation.

"We also raised with the minister the fact that we are fully committed to ensuring that both SAA and SAX are restructured, and in this regard, that government should consider the capitalisation of both institutions if we are to get out of the crisis," the unions said.

"During the next 48 hours, various further engagements will continue between labour and government on a technical and legal basis to find an appropriate solution which will be capable of constituting a constructive input towards the finalisation of a business rescue plan capable of adoption by all stakeholders."