WASHINGTON—The Justice Department on Thursday sued to block the tie-up of Hewlett Packard Enterprise and Juniper Networks, a $14 billion deal that would join the second-largest and third-largest providers of wireless networking solutions for large corporate customers.

The US Department of Justice has sued to block Hewlett Packard Enterprise’s $14 billion deal to acquire networking gear maker Juniper Networks, arguing that it would stifle competition, according to a complaint filed on Thursday.

Juniper Networks stock fell Thursday after the Justice Department moved to block a planned acquisition of the networking company by Hewlett Packard Enterprise.The Justice Department filed a complaint in California district court that seeks to block the merger on antitrust grounds.