As we know the Catholic Church is a major antagonist to Americans against mass immigration. It's important not to distinguish between 'legal' and 'illegal' immigration. The results are the same with respect to unemployment, housing, small business, crime, schools.. The Church claims they are doing the "Humane" thing. It needs to be pointed out that millions of Americans losing their jobs, businesses, homes and health care is hardly "humane". There are of course other reasons but the fore mentioned is the most emotional. And we know, emotion trumps reason in 2014.
I could do this with freeway banners and local signage in front of the churches. The Church, IMO will never respond to any critique injecting the notions of right vs. wrong or moral vs. immoral, if you like.
The answer would $$$$. It's the only thing just about anyone cares about anymore. Therefore, along with the critique of the Catholic Churches policies, a more focused activism could be asking members to do one of the following.
1.) Leave the church for one that does not encourage mass immigration. 2.) Stop making donations to the church. Leave a note why in the collection plate.
Here's an example. 
And 
But with the letters thicker and larger streaming across the near length of the highway... pointing to a website with boycott and church in the url.