The U.S. Justice Department has sued to block tech giant HPE from acquiring Juniper Networks, the networking firm, citing antitrust concerns.

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.

DOJ cited reduced competition in the wireless market as the biggest problem with the proposed $14 billion sale of Juniper Networks to Hewlett Packard Enterprise. The vendors say they plan to “vigorously defend the transaction in court.