Tens of thousands of South Africans have marched in protest over new tolls on roads in what unions says is "the first warning shot" to government. The Cosatu labour federation says the proposed system will hurt the poor - and has threatened more nationwide rallies if it is not scrapped. The ruling ANC says the impact of the road tolls on the poor are exaggerated. The protests were also directed against labour brokering, when agencies hire workers on short-term contracts. The marches, organised by Cosatu (Congress of South African Trade Unions), took place in 32 towns and cities across South Africa. "We have come to here to fire the first warning shot," Cosatu leader Zwelinzima Vavi told marchers who brought the central district business in Johannesburg to a standstill for most of the day. "And in our chamber, there is still a lot of bullets." 'Highway robbery' It was one of the biggest marches in recent years, and looked like the mass demonstrations against the apartheid system during the 1980s and 1990s, says the BBC's Milton Nkosi in Johannesburg. The atmosphere was good-natured, he says, with marchers singing, chanting and waving placards that read "labour broking equals modern day slavery" and "stop E-tolling, it's highway robbery". Electronic tolling is planned for roads between Johannesburg and the capital Pretoria. "The tolls will put a burden on the poor," Mr Vavi told reporters ahead of the marches. "We're saying to the government, we remain open to talk to you. Call us, we will come running to find a resolution." The government upgraded existing motorways in and around Johannesburg for the 2010 football World Cup. It says the work was not free, and it now wants the electronic tolling system to retrospectively finance the roads. The introduction of the tolls has already been delayed several times, after companies warned the fees would raise the cost of doing business. The ruling party said it has already responded to concerns that the tolls would hurt the poor by exempting from paying buses and taxi vans that carry commuters in and out of major towns. South Africa's government has said it also capped monthly fees on the new tolls at $70 (£45) - but correspondents say commuters may already be paying the almost same amount for older toll routes. Flexing muscles Cosatu also wants to see the end of the system of labour brokering - which, it says, means workers get paid low wages and are not entitled to full employment benefits, such as maternity leave. Our correspondent says Cosatu estimates nearly one million people in South Africa are employed through brokers. Wednesday's marches were also about Cosatu flexing its muscles, he adds, and showing the ANC (African National Congress) that although the two are allies, the union federation independently enjoys a great deal of support among South Africa's workers. The ANC - which has been in power since the end of apartheid in 1994 - has been criticised for not doing enough to lift more black South Africans out of poverty. Unemployment in South Africa stands at about 40% and is much higher among young people.