Josh is right, 45auto.
If the operator in question is throwing harmonics and/or spurs on other bands, it will gain the attention of the feds quicker. The 4th harmonics of the CB band runs from 107.86 MHz (107.9 MHz effectively) to 109.62 MHz (109.6 MHz or 109.65 MHz effectively, the VOR band uses 50 kHz steps from 108.000 MHz to 117.950 MHz). 27.025 MHz (CB channel 6) drops its 4th harmonic right on 108.1 MHz, 5th harmonic on 135.125 MHz, 6th on 162.150 MHz...
The 4th harmonics can cause serious interference with the aircraft navigation service (VOR) in the 108.0 MHz - 117.95 MHz range. The 5th harmonics can cause serious interference with aircraft communications in the 118.000 MHz - 136.975 MHz range, specifically 134.8 MHz - 137.025 MHz. Since CB radio uses AM mode and the VHF aircraft band uses AM mode...the source of the interference will likely get noticed pretty quickly. If he's running that dirty of a setup he's probably causing interference all over the bands. Aircraft communications are considered "safety of life" communications and the FCC and FAA will get involved.
All it takes is a few milliwatts (or even microwatts, depending on the antenna used and how close the transmitter is to air traffic) to cause issues with the VHF air band.
Prior to the digital TV conversion, the obvious issue as far as CB harmonics go is that the 2nd harmonic of 27 MHz is right on TV channel 2 (54 MHz - 60 MHz) and AM signals cause massive interference to analog TV signals. z
That aside, a strong AM CB signal can also get into all sorts of electronics (stereo systems, computer speakers, headphones, guitar amplifiers, PA systems, VCRs, entertainment systems, etc. etc.) it's not uncommon for a strong AM CB signal to be heard coming out of a speaker (after all, all you need is a diode to act as a detector if the signal is strong enough).
I did a series of tests a few years back with a home built 11 meter beacon transmitter. It did in the 50-100 milliwatt range and was connected to a dipole antenna mounted in an attic. It was a simple AM transmitter modulated with a 1000 Hz tone generator. Crystal controlled on 27.500 MHz (for initial testing anyway, I eventually played with other frequencies - once I got my hands on a bunch of 26 MHz - 27 MHz crystals) it made a nice carrier signal with two tones 1 kHz up and 1 kHz down from center frequency 27.501 MHz and 27.499 MHz = perfect for doing range testing with a mobile radio in SSB mode.
Anyway, the transmitter's 1 kHz tone could easily be heard coming out of the neighbor's hi-fi system's speakers and my roommate's computer's speakers. Sooo...that got noticed pretty quick. The installation of a low pass filter on the transmitter and several RF chokes on the speaker wire solved the problem.