Labor - agency.
Employer's membership in trade negotiating organization sufficed to bind it to the CBA, even though written authorization to bind the employer was never issued.
Secondary certification writings incorporated the unexpired CBA.
http://www.ca6.uscourts.gov/opinions.pdf/15a0301p-06.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.