See Post 114. Just FYI.
I don't doubt that FR members have been audited. I'm one of them.
The problem is proving that someone was chosen specifically because they are a member of FR, or even that it wasn't the reason.
With a sufficiently large sample of US residents, you are almost certain to find someone that has been audited in the past two decades.
As you posted earlier, people HAVE been targeted for contributing to conservative organizations. It's far more likely there is some overlap with FR members, and that was the real reason.