U.S. lawmakers and defense officials are concerned as more tests on the F-35 joint-strike fighter reveal more complications than they thought.

Defense News reports the concerns stem from the testing of the new Martin-Baker US16E ejection seat system, which, testers discovered, may put pilots at risk of fatal injury. During the tests, ejections performed during low-speed flights showed test dummies snapping their necks.

Test results revealed that when lighter pilots are operating the F-35, the Martin-Baker seats rotate too much. The U.S. military now prohibits pilots weighting under 136 pounds from operating the F-35.

In response to the potentially grim test results, some lawmakers are calling for increased oversight of the joint-strike fighter program. Rep. Jackie Speier, D-Calif., a member of the House Armed Services Committee, said the Pentagon is erroneously rushing the program.

"We're seeing these flight restrictions because the F-35's ejector seats weren't tested to the level they would be on a normal aircraft," the congresswoman said. "This is yet another example of the kind of procurement malpractice we should be avoiding."

The F-35 continues to amass mixed reactions and skepticism as more governments move to procure the aircraft.The ejection seat issue is just the latest setback for the F-35. Pentagon officials stated the joint-strike fighter was not yet "combat ready" in September, despite Marine Corps testing officials claiming the opposite.

The F-35 is Lockheed Martin's winning design of the Joint Strike Fighter program, which Vanity Fair called the most expensive military weapons system in history.