Two U.S. senators have asked the Department of Justice to take tougher action against Boeing executives by holding them criminally accountable for safety issues that have impacted its airplanes.

In a letter dated Wednesday and sent to Attorney General Merrick Garland, Democratic Sens. Elizabeth Warren of Massachusetts and Richard Blumenthal of Connecticut said the department's past efforts to effect change at Boeing have failed "because of its continued refusal to criminally prosecute responsible individuals."

"For too long, corporate executives have routinely escaped prosecution for criminal misconduct. This coddling comes at the expense of customer and worker safety, and it must end," the senators wrote. "We therefore urge you to carefully review the behavior and potential culpability of Boeing's executives and hold criminally accountable any individuals that have promoted a culture at the company that disregards passenger safety in violation of federal laws and regulations."

Boeing declined by email to comment.

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The senators' letter comes ahead of a federal hearing next week over Boeing's agreement to plead guilty to conspiracy in connection with the 737 Max jetliner, two of which crashed, killing 346 people.

Families of some of the passengers killed in the crashes object to the agreement. They want to put Boeing on trial, where it could face tougher punishment.

The Justice Department argued in court filings that conspiracy to defraud the government is the most serious charge it can prove. Prosecutors said they lack evidence to show that Boeing's actions caused the crashes in Indonesia in 2018 and Ethiopia in 2019.

Relatives of victims and their lawyers have called the settlement a sweetheart deal that fails to consider the loss of so many lives. Some of the lawyers have argued that the Justice Department treated Boeing gently because the company is a big government contractor.

The agreement calls for Boeing to pay a fine of at least $243.6 million, invest $455 million in compliance and safety programs, and be placed on probation for three years.

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Boeing — which is also grappling with a nearly three-week-long strike of 33,000 machinists — has faced a series of safety concerns in the past year.

Just last week, federal safety investigators issued urgent recommendations to Boeing and the Federal Aviation Administration after determining pedals that pilots use to steer 737 Max jetliners on runways can become jammed because moisture can leak into a rudder assembly and freeze.

And earlier this year, a door plug blew off a 737 Max minutes after an Alaska Airlines flight took off from Portland, Oregon, leaving a gaping hole in the plane and creating decompression so violent that it blew open the cockpit door and tore off the co-pilot's headset. The plug had been opened at a Boeing factory to let workers fix damaged rivets, but bolts that help secure the panel were not replaced when the plug was closed.

There were no major injuries, and the pilots were able to return to Portland and land the plane safely.