The Federal Aviation Administration will reportedly force Boeing (BA -2.87%) to modify or move wire bundles in the grounded 737 MAX airplane, a fresh setback for the aerospace giant as it attempts to return the plane to service after nearly a year.

We are coming up on the one-year anniversary of the March 10, 2019, crash of an Ethiopian Airlines 737 MAX that killed all on board and prompted regulators to pull the plane out of service. Boeing has been working with U.S. and international regulators on fixes, but it has been a long, drawn-out process that has taken the aerospace company much longer than it initially anticipated.

The 737 MAX flying above the clouds.

Boeing's 737 MAX. Image source: Boeing.

Boeing had hoped to resolve the issues that caused the crash primarily via software changes and added pilot training, but the FAA has concerns that some of the plane's wiring could be prone to a short circuit, which could cause pilots to lose control. The FAA formally rejected Boeing's proposal to not move the wiring, saying the current setup is not in compliance with certification standards, CNBC reported late Sunday..

The decision comes just days after a Congressional committee slammed Boeing over the "culture of concealment" that lawmakers claim contributed to the crashes. Congress has also been critical of the FAA being too cozy with Boeing in the past.

A Boeing spokesperson told CNBC that the company remains in discussions with the FAA but said that even if the bundles need to be modified it would not alter the company's timetable for returning the plane to service. Boeing and its airline customers are hopeful to have the 737 MAX flying by the second half of this year.