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.

U.S. government regulators sued to block Hewlett Packard Enterprise’s $14 billion acquisition of rival Juniper Networks on Thursday, saying the combination would eliminate competition, raise prices and reduce innovation.