Graham said he was concerned the NLRB's case against Boeing was used to prod the company to make the deal with the IAM union. He called for a congressional investigation into that possibility.
"A congressional investigation to answer questions about the NLRB’s role, attitude, and relationship with the parties is definitely warranted," he continued.
Graham added that he would continue blocking nominations to the NLRB "until we get satisfactory answers regarding their role in this entire saga.
"Given its recent actions, the NLRB as inoperable could be considered progress,” he said.
The agency is set to have just two members at the beginning of next year, which would render it in unable to issue rulings.