Striking truck drivers blocked key Mexican transport arteries on Thursday, jamming vital highways to protest lawlessness on the roads that has led to a rise in robberies and extortion.

Traffic on at least nine highways was affected by the protests, according to local media reports.

Rafael Ortiz, leader of transport group Amotac, told local media that more strikes could be called if the government does not meet their demands.

Ortiz urged the government to boost security, noting that between one and two truck drivers are killed every month on the roads due to the lack of safety.

The road blockades erected by the striking drivers are “unfounded and unjustified,” Mexico’s government said in a statement on Thursday, adding that Amotac representatives decided to stop negotiations on Wednesday even as progress was being made.

In a statement, Amotac, the drivers’ group leading the strike, called on the government to ensure safety on the roads as well as end fees to transit certain highways and municipal tolls for loading goods, among other measures.

Mexico’s government said some agreements had been reached with other organizations to improve safety, such as strengthening federal inspections of double-articulated tractor-trailers, and the deployment of 600 officials of the National Guard and 2,000 radio patrol cars.

The government said in its statement it was still open to dialogue.