Taken from a different view. A civil suit is filed. An IRS whistleblower is not yet filed. Later it appears IRS violations are found. They are raised to the other side. The other side files a counter suit for defamation. The violations are clear. If at any point the plaintiff says we are now going to the IRS I would assume that is not blackmail. The public good is benefited from the IRS knowing. The plaintiff is not asking for money only placing them on notice.