The NBA filed a complaint with the NLRB claiming that the Union's threat to decertify was evidence that the union failed to bargain in good faith. The league claimed the union threatened to decertify as a union more than two dozen times. The union was using this as a negotiation tactic. The NBA's filings probably will not have an effect on the negotiations as legal proceedings will take far too long to be resolved.
See "In Defense of Lockout, N.B.A. Sues the Union", Ken Belson, The New York Times, August 2, 2011