Shares of Apple sunk 4% Tuesday after reports that the company is facing engineering challenges with its highly anticipated foldable iPhones.

“Apple and the supply chain are working under a pressured timeline and the current solutions are not enough to completely solve the engineering challenges. … More time is needed,” a person familiar with the situation told Nikkei Asia.

Apple, which celebrated its 50th anniversary last week, has announced four new iPhone models at its September launch event every year since 2020. The foldable phone was expected to launch alongside the iPhone 18 in September 2026, but delays could change that timeline.

CNBC reached out to Apple for comment.

April through early May is seen as a critical time for the iPhone maker to resolve engineering issues ahead of production, according to Nikkei.

Samsung, Apple’s top rival in the U.S. smartphone market, launched its first foldable phone in 2019. iPhones are a key money maker for Apple, driving over half of the company’s $143.8 billion reported revenue for the first quarter of fiscal 2026.

Nikkei reported that the memory chip crunch, which has made it hard to meet growing iPhone demand, is not playing a role in the foldable phone delay.