I think there's much less power over people who don't have security clearances. In the cases you describe, the companies are government contractors whose employees probably have clearances, and have agreed to all sorts of checks (and are required to follow certain procedures as a result of getting their clearances). The companies most likely agree to those clean-up visits anyway, if they want to keep getting government contracts, so it's not necessarily even using the government's law-enforcement power.
If leaked information gets to a normal civilian who's never gotten a security clearance, though, I don't think that's illegal, if they didn't have a hand in leaking it themselves. That was basically the outcome of the Pentagon Papers case: that the people who leaked the papers to the NYT could be prosecuted, but the NYT couldn't be stopped from republishing them. Not that that'll necessarily save someone from getting hassled.
If leaked information gets to a normal civilian who's never gotten a security clearance, though, I don't think that's illegal, if they didn't have a hand in leaking it themselves. That was basically the outcome of the Pentagon Papers case: that the people who leaked the papers to the NYT could be prosecuted, but the NYT couldn't be stopped from republishing them. Not that that'll necessarily save someone from getting hassled.