Powerful agribusiness interests are trying to force through a major change in Brazil's vital forest management law. A bill just passed by the country's parliament would seriously weaken protections for the world's largest rainforest. Now, a veto from President Dilma Rousseff is the only way to head off this disastrous change.

A global resource at risk

More than two-thirds of the world's fresh water is in the Amazon basin, and 20% of the planet's oxygen comes from there. As Brazil's economy grows, pressure is mounting to clear rainforest for soya beans, beef cattle and other agricultural uses. But since 2009, stronger enforcement of forest protection laws has dramatically slowed deforestation.

The bill just passed in Brazil's Chamber of Deputies would, among other changes:

• Relax rules that make farmers preserve as much as 80% of their land.
• Ease restrictions on forest clearing near riverbanks and on hillsides.
• Reduce the amount of land that has to be reforested.
• Offer an amnesty for past illegal deforestation.

The bill's supporters say the changes would free Brazil's farmers from burdensome rules that have been costing jobs and money. As one key lawmaker put it: "We intended to create a text that would not expel a single producer nor a single worker from the Brazilian countryside."

More than money at stake

With the United Nations Rio+20 climate change conference coming up next month, this is a particularly inappropriate time for the hosts to backslide on rainforest protection. Environmental groups and concerned citizens in Brazil and across the world are focusing their efforts on persuading President Dilma Rousseff to veto changes to the law. A powerful "Veta, Dilma" ("Veto, Dilma") movement has sprung up in Brazil.

Even if President Rousseff does listen to the call, it's not a sure thing. Her veto could be overridden by a majority of the Chamber of Deputies – the same lawmakers who made the new rules in the first place.

Take action: Let's make our voices heard before it's too late. Avaaz has joined with Greenpeace and WWF in a petition to tell President Dilma to use her veto pen. Join the global call here.