The largest domestic espionage campaign ever conducted against the American government came from the Church of Scientology. It started in 1967, when the IRS revoked Scientology’s tax-exempt status, ruling that the church wasn’t legitimate and “operated for the benefit of L. Ron Hubbard and his family.”
The church refused to pay up. They began a massive campaign to find information on the IRS to use it against them. They planted bugs in the IRS conference room. They sent undercover agents to get jobs at the IRS so that they could steal and copy government documents.
By 1977, Scientologist George Bennett Wolfe was caught using a fake ID to get into a courthouse, where he stole and made copies of thousands of government documents. Over the next few years, 11 more Scientologist agents were caught committing similar crimes, arrested, and jailed.