The relevant statute only grants federal jurisdiction over claims of CBA violations; a suit alleging that the provision is void for lack of formation under state law therefore does not state a claim under the statute.
Dissent: It can be construed as a request for declaratory judgment as to the plaintiffs own alleged violation of that provision of the CBA.
http://cdn.ca9.uscourts.gov/datastore/opinions/2018/06/20/16-55451.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.