Federal regulators discovered new risks presented by the Boeing 737 Max on Wednesday.

The U.S. Federal Aviation Administration (FAA) said the new risk was discovered during a simulator test last week, according to Reuters.

The FAA said in a statement it recently found a “potential risk that Boing must mitigate,” without elaborating on what the newly discovered issue is.

“The FAA is following a thorough process, not a prescribed timeline, for returning the Boeing 737 Max to passenger service. The FAA will lift the aircraft’s prohibition order when we deem it is safe to do so,” the FAA said.

Boeing issued a statement regarding the new discovery and said the FAA asked the company to address the issue through additional software changes.

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"Boeing agrees with the FAA's decision and request, and is working on the required software. Addressing this condition will reduce pilot workload by accounting for a potential source of uncommanded stabilizer motion," Boeing said.

The new issue will set Boing back from conducting its certification test flight until at least July 8, and the FAA will likely spend several weeks reviewing results before deciding whether to return the plane to service, according to Reuters.

The popular 737 Max was grounded after two fatal crashes earlier this year. Boeing has been working on upgrades since.

"Boeing will not offer the 737 MAX for certification by the FAA until we have satisfied all requirements for certification of the MAX and its safe return to service," the company said in its statement.