efe-epaSao Paulo

Brazilian organized labor turned this year's International Workers' Day into a public outcry to demand the release of former President Luiz Inacio Lula da Silva, who has been serving a prison sentence on a corruption conviction since April 7.

The seven largest unions organized a thousands-strong demonstration in the southern city of Curitiba, near the police precinct where Lula is serving a 12-year and one-month sentence.

This is the first time since the end of Brazil's 1964-1985 military regime that these unions have marched together on May Day with one common slogan - "Defending rights and demanding Lula's release."

The demonstration centered on demanding the release of the former two-term president, a metalworker who forged his leadership in Sao Paulo's labor union movement, although other issues also came to the fore, including the austerity policies of current head of state Michel Temer, whose approval rating stands at 6 percent.

"Workers have never been under such attack, with a loss of rights and rising unemployment and poverty. In addition, we now see Brazil's best former president become a political prisoner," Wagner Freitas, head of the giant CUT labor federation, said.

May Day marches were also held in Sao Paulo, Brazil's largest city, as well as in Rio de Janeiro, Brasilia, the country's capital, and cities in at least 10 other states.

Lula, 72, who continues to lead the polls ahead of October's presidential election, was convicted for allegedly accepting an apartment in exchange for helping Brazilian construction company OAS obtain lucrative contracts from state oil company Petrobras, in the context of a larger $2 billion corruption scandal centered on the oil giant.

The former president maintains his innocence, while prosecutors have failed to produce any evidence that Lula was the legal owner of the residence or even that he ever set foot inside.

"There is a growing awareness that this was all just a maneuver to prevent Lula from running in the 2018 elections," former Cabinet minister Fernando Haddad said.

President Temer's policies were also deplored during Brazil's May Day marches, including a constitutional ceiling on government spending and an overhaul of labor laws that is expected to lead to lower wages amid an unemployment rate of 13.1 percent.

Tuesday's demonstrations also included calls to end violence against leftist movements and activists, just two days after a shooting attack against the "Free Lula" protest camp in Curitiba left two people injured, and a little over a month after Rio de Janeiro city councilor Marielle Franco was assassinated.