A small group of Boeing engineers who perform key safety tasks are raising concerns about their ability to work free of pressure from supervisors, and their comments are prompting federal regulators to take a broader look into the company’s safety culture.

The employees are deputized to approve safety assessments and handle other jobs for the Federal Aviation Administration, making their independence from company pressure critical.

According to an FAA letter, one of the employees said, “I had to have a sit down with a manager and explain why I can’t approve something.” The worker indicated that the company shopped around for another employee in the engineering unit.

Another employee reported consternation by managers when engineers find fault in designs of components because that can cause delays in delivering airplanes.

The FAA's initial investigation ran from May until July. An FAA official described it in an Aug. 19 letter to Boeing's leader of safety and aircraft certification. The Associated Press obtained a copy of the letter, which was first reported by The Wall Street Journal on Tuesday.

“We take these matters with the utmost seriousness, and are continuously working to improve the processes we have in place to ensure the independence” of employees who work on behalf of the FAA, said Boeing spokeswoman Jessica Kowal. She said those employees “must be accorded the same respect and deference that is shown" to FAA personnel.

The FAA surveyed 32 of the roughly 1,400 Boeing employees who are deputized to work on the FAA’s behalf. Of those surveyed, one-third raised concerns. The FAA said in the letter to Chicago-based Boeing that it will follow up by surveying all employees in the unit.

The FAA examination raises further questions about a longstanding practice of relying on employees of aircraft manufacturers to perform safety-related work, including analysis of critical aircraft systems. The policy is supposed to take advantage of the employees' specialized knowledge, and the companies are supposed to give those workers authority to perform the safety-related functions without interference.

However, findings from Boeing “indicate the environment does not support independence” of the employees, Ian Won, an FAA official who helps oversee Boeing, wrote in the letter to the company.

The FAA's policy of relying on safety assessments by industry employees, called organization designation authorization, came under intense scrutiny after two deadly crashes involving the Boeing 737 Max. Investigations determined that key people at the FAA were largely unaware of an automated flight-control system that played a role in the crashes.