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.

The Justice Department on Thursday sued to block Hewlett Packard Enterprise from buying Juniper Networks for $14 billion. Why it matters: This is the first antitrust case filed by the Trump administration,