(Reuters) - Electronic storage device maker Seagate Technology Plc said its fourth-quarter revenue is expected to have missed its forecast as a quality issue at a supplier affected production in its enterprise disk drive unit.

The company, which competes with Western Digital Corp, said shipments fell by about 1.5 million units to about 66 million for the June quarter, squeezing gross margins.

Seagate expects an adjusted gross margin of 33.6 percent.

The company now expects to report revenue of $4.5 billion. It had forecast $5 billion.

Analysts on average were expecting revenue of $4.88 billion, according to Thomson Reuters I/B/E/S.

Shares of the company were down 6 percent at $23.62 in trading after the bell. They closed at $25.08 on Thursday on the Nasdaq.

(Reporting by Chandni Doulatramani in Bangalore; Editing by Don Sebastian)