On May 26, Deere & Company issued a report to the FCC notifying of how the LightSquared signal would substantially interfere with GPS signals, registering impact as far as 22 miles from a transmitter. Additionally, Deere has not discovered a "practicable technical solution" to the problem. Their report includes an informative graphic that illustrates how, of all GPS receivers, modern high precision receivers would be impacted most adversely. Deere states that allowing LightSquared to operate their system as proposed would create massive interference to the StarFire satellite-based augmentation system that Deere provides through NavCom, with the risk of serious harm to the U.S. agriculture industry.
See the full GPS World article here, or use download a PDF of John Deere's report.