Public servants cannot have private business interests, the Congress of South African Trade Unions (Cosatu) tenth national congress in Midrand heard on Wednesday.

"We continue to insist that public representatives must choose between being public representatives and live within their salaries, or must choose business. You can't be both," general secretary Zwelinzima Vavi said in his political report.

"A public representative cannot be a business person at the same time," he said.

In the ensuing debate, the Cosatu affiliated South African Municipal Workers' Union (Samwu) called for corruption to be "declared a crime against humanity".

Citing as an example the North West, where many public servants have recently been suspended, Samwu said corruption perpetuated poverty, irrespective if whether it took place in the public or private sector.

It was therefore necessary to deal harshly with those found guilty of corruption.

Vavi acknowledged the government's tough stance on corruption, but said more needed to be done.

He again called on Cabinet Ministers with cars worth over R1-million to return them.

However, there was some resistance from the congress on this matter.

The South African Democratic Teachers' Union said the matter should not be "personalised".

The union said the fundamental question was expenditure and that should be the focus.

Cosatu recently criticised Cabinet Ministers for spending a lot of money on luxury vehicles.

This, after the South African Communist Party's general secretary and Higher Education Minister Blade Nzimande bought a R1,1-million BMW.

While the National Union of Mineworkers said that returning the cars was "not practical", it agreed with "the general message that those in public office do not create a gap between themselves and their constituency".

Samwu urged Cosatu to resolve that the Auditor General "must tighten its screws" so that public servants were not able to "fiddle with the auditing process", currently a problem allowing corruption to take place.

The resolution to tackle public servants with business interests and corruption was passed.

The debate on the political report continues, with a resolution on the planning commission. A response by African National Congress secretary-general Gwede Mantashe is expected to contribute to the debate.