Boeing has turned over instant messages from 2016 that suggest the company may have misled the Federal Aviation Administration about a safety system on the 737 Max, according to a report from Reuters.

The FAA said on Friday that Boeing had told it about the message this week but they had been discovered “some months ago,” Reuters reported.

“Sources told Reuters the Boeing internal messages raised questions about the performance of the so-called MCAS anti-stall system that has been tied to the two fatal crashes in five months. Boeing declined to immediately comment,” the news agency said.

“The FAA is also disappointed that Boeing did not bring this document to our attention immediately upon its discovery,” the agency said in a statement to CNBC. “The FAA is reviewing this information to determine what action is appropriate.”

Shares of Boeing fell 4 percent when the news broke on Friday.

Boeing’s chief executive, Dennis Muilenburg, was removed as chairman of the company’s board last week. He is scheduled to testify before Congress on October 30.