The Justice Department sued to block Hewlett Packard Enterprise's $14 billion acquisition of rival Juniper Networks on Thursday, the first attempt to stop a merger by a new Trump administration that is expected to take a softer approach to mergers.

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 Enterprise shares are trading lower Thursday after the U.S. Department of Justice (DOJ) filed an antitrust lawsuit to block its proposed $14 billion acquisition of Juniper Networks.