[Unionists take part in a demonstration called "National Day in Defense of Workers' Rights" in Sao Paulo on April 7, 2015 (AFP Photo/Nelson Almeida) ]

Brazilian police and demonstrators clashed Tuesday in the capital Brasilia during a march opposing a congressional bill to increase outsourcing in the workplace.

The country's CUT union federation called protests in a number of cities, including business hub Sao Paulo, "in defense of working rights."

Police cordoned off access to the Congress building and fired tear gas as some marchers tried to break through their ranks.

At least two demonstrators were hurt, police told AFP, adding one man was arrested.

According to the union, some 6,000 marchers answered their call to protest in Brasilia -- though police put the figure at 2,000, compared to some 500 in Sao Paulo.

Other social movements, including a movement for homeless people, backed the marches ahead of an expected vote in Congress on a proposed measure which lawmakers have kicked back and forth for several years.

The legislation would allow outsourcing to cover a wide variety of activities in both the private and public sectors.

"The bill withdraws, in practice, rights won by workers with difficulty and gives bosses the legal right to employ as they see fit," the CUT complained, calling for protests by its supporters. Wider anti-government protests are scheduled for Sunday.

Opponents of the bill maintain it would have a greater effect on workers than austerity measures being implemented by the government of President Dilma Rousseff, who is struggling to refloat a sinking economy.

If the bill is approved, it will go forward to the senate.

"We are worried -- we think the bill is going to go through and afterwards it will be up to President Dilma to veto it," Hilton Marioni dos Santos, leader of water and sanitation union Sindaema, told AFP.

He forecast that given the current frenzied political climate stemming from a huge corruption scandal at state oil firm Petrobras Rousseff might find it difficult to defy Congress.

"We are not here to topple Dilma but to ask for dialogue. Workers' rights are at stake," Adi dos Santos Lima, CUT Sao Paulo branch president, told AFP.

The CUT estimates that 12.7 million jobs -- just over one in four -- are currently outsourced in Brazil.