Democratic presidential candidate Sen. Bernie Sanders says American Airlines' negotiating tactics with maintenance workers is "nothing more than corporate greed at its worst."

Sanders had harsh words for the Fort Worth-based airline in a letter to CEO and chairman Doug Parker on Wednesday, making him the latest politician to weigh into the ongoing contract dispute between the company and maintenance workers.

"If American Airlines has enough money to buy back $15 billion of its own stock, it certainly has enough money to pay its union workers a decent wage with good benefits," Sanders wrote in the letter posted to Twitter Wednesday.

American Airlines mechanics are the latest union workers to win support from Sanders. Earlier this week, he walked picket lines with striking United Auto Workers members in Detroit. It's also not the first time Sanders has gone after Parker, criticizing the airline leader at a union event in April.

In August, a group of East Coast lawmakers, including Rep. Alexandria Ocasio-Cortez, penned a similar letter to American Airlines and criticized the company for outsourcing maintenance jobs.

"American performs more maintenance and fleet service work in-house than any other U.S. airline, including at our maintenance bases in Tulsa, Charlotte, and Dallas-Fort Worth," said American Airlines spokesman Joshua Freed. "We're proud to offer these high-quality, well-paying jobs with good benefits."

The unions representing 30,000 American Airlines maintenance workers have been locked in a tedious contract dispute with the company since 2015. The two sides met with federal mediators this month.

The dispute is so bad that American Airlines sued mechanics in federal court for slowing down work on overnight maintenance, causing thousands of delays and hundreds of cancellations. American won the lawsuit.

One of the biggest contract disputes is a plan for American to outsource as many as 5,000 jobs to contractors, according to International Association of Machinists officials. American says it's offering job protections and raises to mechanics now working at the company.

Sanders, a self-described democratic socialist, criticized American for suing its workers.

"American Airlines must do the right thing and agree on a fair contract to end over three years of limbo it has forced its workers to endure," he said.

The association representing workers from legacy American Airlines and U.S. Airways have complained the company is outsourcing jobs to foreign maintenance facilities, sacrificing quality and safety for lower costs. Sanders took the side of the unions.

"American Airlines must stop risking the safety of the flying public and its own workers just to make even more profits," his letter said.