Indigenous groups blocked a highway just outside the Brazilian city of Sao Paulo and burned tires in the early hours of Tuesday to protest a draft bill that could hamper efforts for indigenous ancestral lands to gain protected status.

Protestors could be seen burning tires, firing arrows and throwing objects at the riot and military police, who arrived at the scene soon after the start of the protest, using water cannons and tear gas to disperse the small crowd.

The bill, known as PL 490/2007, strips the environment and indigenous people ministries of some powers, weakening their oversight of environmental protections and the demarcation of indigenous lands.

The bill will be up for a vote in Brazil’s lower house in the coming days.

Indigenous groups from across the country also planned protests in the capital Brasilia, where President Luiz Inacio Lula da Silva is meeting with several other leaders from across South America.

While the bill does not impact fully recognized indigenous territories, it would affect territories that are under claim.

Rights groups warn that the bill would “prevent Indigenous communities from obtaining title of their lands if they were not physically present on them on October 5, 1988, the day Brazil’s current Constitution was adopted,” writes Human Rights Watch.

Indigenous protesters closed a highway in Sao Paulo on May 30.

“Indigenous peoples who were expelled from their territory before October 1988 and cannot prove they were involved in an ongoing dispute over their claim on that date would not be able to secure legal recognition of their lands,” Human Rights Watch wrote in a statement.

“Choosing an arbitrary cutoff date and refusing to recognize ancestral lands claimed after that date is not in line with international standards,” it added.

Lula has promised to repair the damage to the Amazon caused by his predecessor, Jair Bolsonaro, under whose presidency deforestation surged. Last month, Lula recognized six Indigenous territories, Reuters reports.

But he has had to face a hostile congress, which approved expediting the bill’s review process last week. If the bill passes the lower house, Senate will have to approve it before being signed into law by Lula. The president could veto the bill, Reuters reports, but Congress could have enough support to override the move.

If the bill passes, it could tarnish Lula’s climate ambitions. “If Lula loses this battle in Congress, it will represent yet another political defeat for his administration and display the conservative force he faces,” Bruna Santos, director of the Wilson Center’s Brazil Institute, told CNN.