There have been rare cases of the President not signing an agreement, but those are extreme cases. The most recent case that I can remember would be the CCAir case, in which the agreement was negotiated by the CCAir MEC outside of the requirements set by the Constitution & By-Laws for concessionary agreements. Basically, they negotiated a concessionary contract with JO, but JO refused to show any evidence that MAG actually needed the concessions. ALPA doesn't give concessionary contracts without proof that the corporation actually needs it. So, with the MEC acting outside of the bounds set by the C & BLs, Captain Woerth refused to sign the contract.