See, Todd Palin is a member of the United Steelworkers union. The United Steelworkers union is spending millions of dollars in union dues, to “play a key role in electing Obama.” Since Alaska is a compulsory union state (as is Pennsylvania) Palin’s dues are mandatory.
A recent Supreme Court ruling allows any union members to opt out of union dues unrelated to collective bargaining, but the process is often challenging (and not well known among union members).
The National Right to Work Legal Defense Foundation has the details, as well as free legal advice for other union members who may not want their union dues going to support certain political candidates. (This applies to members of the AFL-CIO, the SEIU, the NEA, and AFSCME in particular)