The lawsuit said that the combination of businesses would eliminate competition, raise prices and reduce innovation.

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.

Hewlett Packard is set to merge with Juniper for $14 billion. However, the U.S. Justice Department is suing to block the merger.