Collective Bargaining Agreements

Speaking in terms of an "open Shop".

Can a union negotiation commitee place wording into a contract that states any and/or all bargained matters be applicable to "Union Members Only"?

Such as a pay increase only given to union members?

Is there any Legal Statute or Precedence that covers this.

Since NLRB vs. General Motors states no one HAS to join a union, is there something that states what is bargained is only applicable to union members?

http://laborlaw.itags.org/q_employment-labor-law_12061.html