Just observing here to this point and have nothing to do with this tactic, it appears misguided by being sold to the Bank of Montreal and no longer has any desire to support the Walker camp. Whilst there is some level of irony as you pointed out, it does cut both ways. M&I employees weren't looking out for the public union workers and the company actually contributed to what's been happening to them.
It's pretty common for people to take their business to whom they consider their friends and away from and/or against their foes. The common sense of that is self-evident. People also do that in the hopes of influencing the decisions a company makes. It's pretty par for the course and can be effective. I do this myself. For example, I don't buy Citgo gasoline/petrol if I can avoid it. That's because I don't like what Hugo Chavez does to the US and others and therefore don't wish to put money in his regime's pocket. Obviously that affects US Citgo workers and independent contractors and others choosing to do business with them, but c'est la vie. Citgo workers can go talk to Hugo about changes of attitude.