Boeing has been ordered by U.S. air safety officials to detail the state of its 737 MAX's subsystems in light of the plane's recently uncovered electrical grounding problems.

Boeing is being asked to prove that the plane's subsystems will not be affected by the issue flagged in three areas of the jet last month, with the U.S. Federal Aviation Administration (FAA) calling for documentation from the company.

The latest order is expected to inject new uncertainty over the reinstatement of the company's jets by the FAA. According to sources familiar with the matter, the flagged issues have resulted in the suspension of nearly a quarter of the company's 737 MAX fleet.

The same sources said the latest issue could delay the approval of the company's best-selling jetliner by months. Boeing previously said it would release updated service bulletins regarding the problem, including fixes and their expectations on when the planes can return to service.

"We continue to work closely with the FAA and our customers to address the ground path issue in affected 737s," Boeing said.

In response to inquiries regarding the latest issue, the FAA said it is continuing to work with Boeing to find a resolution. Last month, Boeing was forced to pull dozens of its jets from service after it found production-related electrical grounding problems with a backup power control unit.

The issue reportedly affected mostly the company's recently built airplanes. Three control units are reportedly affected by the problem, include one near the cockpit, another in the storage rack and another located inside the instrument panel facing the pilots.

Boeing said it has temporarily halted the delivery of new planes due to the problem. Last week, Boeing issued a service bulletin that showed airlines how to fix the grounding issue. Sources said the problem lied within the electrical path designed to maintain safety in the event of a surge in voltage.

The FAA approved the release of the bulletins but requested that Boeing submit additional analysis on the safety of its other subsystems. The FAA plans to review all of Boeing's documentation before it approves any new service bulletins to affected airlines.