Boeing is reworking 50 undelivered 737 MAX jets after a supplier's employee recently found misdrilled holes on some fuselages, a new production snafu for the aircraft manufacturer.
Boeing shares slipped 1.8% in premarket trading on the news.
Spirit AeroSystems, which has been at the center of quality issues affecting 737s, supplied the fuselages.
Boeing said that the issue could delay some deliveries in the near term and that existing 737s can keep flying.
"This is the only course of action given our commitment to deliver perfect airplanes every time," Boeing's commercial chief Stan Deal said in a memo to staff on Sunday.
Boeing said it is finalizing instructions for the rework and expects to know how long it will take in coming days.
Deal said the employee flagged to his manager two holes that may not have been drilled exactly to the jet maker's requirements. Delays will allow the company to inspect and, if necessary, fix any problems, he said.
A Spirit spokesman said the company is aware of the issue and is in close communication with Boeing. Last year, misdrilled holes by Spirit on the aft bulkhead of some MAX jets led to production delays.
Boeing is facing additional regulatory scrutiny after the Alaska Airlines door plug blowout last month. That incident, which also involved a Spirit fuselage, followed a string of issues involving the supplier, none of which led to in-flight incidents.
In the case of the blowout, the jet maker and industry officials increasingly believe Boeing employees failed to put back bolts needed to secure the door plug during production.
Deal also said Boeing has recently instructed a major supplier to hold shipments until all parts meet requirements, a move he said would lead to production delays. A spokeswoman declined to say if Deal was referring to Spirit or a different supplier.
Boeing executives have pledged to review manufacturing practices and root out defects. The company last week said it wouldn't set financial targets for the year as it focuses on improving quality. Investors and airline customers, which already are short on planes, worry that heightened scrutiny and Boeing's efforts to improve its processes could slow deliveries.