WASHINGTON—The Justice Department is investigating whether Huawei Technologies Co. violated U.S. sanctions related to Iran, according to people familiar with the matter, a move that opens a new avenue of scrutiny of the Chinese cellular-electronics giant on national security grounds.

It’s unclear how far the Justice Department probe has advanced and what specific allegation federal agents are probing. A Huawei spokesman declined to comment.

Such a probe raises the stakes for Huawei, which is facing a series of actions by Washington to diminish the company’s already limited business dealings in the U.S. It could also have spillover effects for its much larger business overseas, particularly in Europe.

Analysts said a worst-case scenario could entail Huawei suffering the same fate as smaller Chinese rival ZTE Corp. , which has lost access to U.S.-made components in a similar probe.

Investors on Wednesday sold down shares in some of Huawei’s suppliers, including a group of small optical-technology firms like Lumentum Holdings Inc., after The Wall Street Journal first reported the probe. Qualcomm Inc., which supplies Huawei with chips, also edged lower.