First, I support unions and I absolutely believe that you make more money and get better benefits because you are in a undion.
But, from my perspective there is also an imbalance.
Last I looked, greater than 95% of Teamster PAC money goes to democrats. Certainly, you have a right to contribute as you see fit. But I'm not sure how well that distribution matches the political distribution of the membership.
OK I see where the disconnect is happening.
Teamster D.R.I.V.E. is our Political Action Committee (PAC). It stands for Democrat Republican Independent Voter Education. This is a separate contribution
that a member must pledge via a separate pledge card. So the simple answer is: Don't want any of your money going to Teamster political purposes? Don't sign up for D.R.I.V.E.
As to the 95%, if you read about D.R.I.V.E. they are unaffiliated with any particular party and only are concerned about candidates favorable to Labor issues. This would pretty much guarantee 95% would be Democrats. I'm unaware of any PACs that survey their members to see where their money should go. The PAC adopts a position and you either contribute or don't. I can't stand the environmental movement so none of my donations go to the Sierra Club although I love the wilderness, clean water etc.
About DRIVE | International Brotherhood of Teamsters (IBT)
So to the OP, sleep better knowing your money isn't going directly towards political purposes unless you are a member of D.R.I.V.E. If you happen to be a member, just fill out another card and put your contributions to "$0". Problem solved.
As to the Teamster Magazine, it's purpose is mostly for organizing, then legal notices, and plenty of pro-Labor propaganda which shouldn't be surprising. I might skim through it but if I find something interesting I do my own research instead of relying on it for factual information just as I would any mailer from a campaign, PAC, etc. They posted the covers online here:
Teamster Magazine Archive | International Brotherhood of Teamsters (IBT)
and I'm guessing the current Anti-Romney one is causing the trouble. You have to go back to Jan/Feb 2009 to find Obama on the cover, and he's on the two before that (Nov/Dec Oct/Sept 2008) which makes sense because that is right before the election. Teamsters, just like Police Associations/Unions, Fire, etc will endorse a candidate. I don't think this endorsement means much because other than mailing crap to your home and maybe a robocall or two it's not like Guido is visiting you at midnight to 'encourage' you to vote the right way. I'm sure if you get carpal tunnel from throwing the Teamster rag along with all the other political junk mail in the trash you will have plenty of groups to sue for your injury.