(Bloomberg) -- Mexico President Andres Manuel Lopez Obrador’s $9 billion refinery has been rocked by a labor strike that turned violent when police tried to disperse workers, opening his key energy infrastructure project to fresh criticism.

Mexico’s Energy Minister Rocio Nahle said hundreds of contract workers from ICA Fluor started striking yesterday over internal union politics, but that all the employees have been getting fair salaries and that injuries were minor. She tweeted a statement from ICA Fluor that said armed forces were now guarding the Dos Bocas refinery in the state of Tabasco.

Nahle was responding to local media reports of close to 5,000 on strike and to videos streamed on social media and picked up by newspapers of police lobbing tear gas while workers bled from eye and leg injuries. 

The massive new oil refinery for state-owned Petroleos Mexicanos is key to the president known as AMLO’s goal to strengthen state energy companies and to build jobs in Mexico’s poor south, but it has already received its share of criticism. It’s being constructed during a new era focused on renewable energy, it’s running over budget and behind schedule, and it’s being built in a zone the state oil firm had promised to protect.

Read More: Pemex Is Building Refinery in Green Area It Promised to Protect

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