Guys,
The rules for ratifying a contract, including one with a national portion and local supplements, should be spelled out in you IAM Constitution.
Here in the Teamsters we went to a national agreement (called the National Master) with regional and local Supplements in 1979. However, the two largest locals, 705 and 710, covering Illinois, Indiana and Davenport Iowa are not included. They are seperate bargaining units. Seperate from the National Master, and seperate from each other. Everyone covered by the Master is in the same bargaining unit even though we have regional supplements.
The idea of a national contract was sold as as solidarity and bargaining power thing, but it has been just the opposite. Each individual member is voting on a wide range of issues that he knows little or nothing about, and that don't effect him personally.
The natural tendency is for people to vote "Yes" because they want to avoid a strike. The Union wants "Labor Peace" as much as the company does. Since much of the contract doesn't apply to the individual voter, the natural tendency is to vote "Yes", (or not vote at all,) unless there is some one issue that he is very upset about. The Teamsters also unanamously urge a "Yes" vote. Add to that the lack of information, and lack of time to discuss and debate the language.
Thus the national voting system virtually guarantees a majority "Yes" vote.