Dozens of farmers brought traffic to a halt Wednesday as they blocked access to the Congress of the Union in Mexico City, protesting a proposal to overhaul the National Water Law.

The farmers argue the reform, which includes stricter controls on water concessions and use, threatens their livelihoods and chips away at what they call a fundamental right for all Mexicans: access to water.

Before dawn, caravans of tractors rumbled into the capital, backing up traffic for miles at key entry points. By midmorning, the protesters had massed outside the Chamber of Deputies, demanding lawmakers hear them out.

"There’s an intention to take water away from the countryside and place it in reserve funds for discretionary use," said Elena Burns, a well-known academic and former public official who has spent her career defending the right to water.

As the bill advanced, the tractors continued to ring Congress - a show of force from farm groups intent on stopping the proposal before it reaches the full chamber.

"Defending a right is life. A concession is just a tradable good and that’s where the tremendous corruption within the water authority lies," said Ruben Perez, representative of the Endhó Canal in Hidalgo state.

Agricultural leaders warned they are prepared to escalate, threatening new blockades on highways and at border customs checkpoints that could again bring the country to a standstill.

AP Video by Claudia Rosel, production by Fernanda Pesce