Private investigators working for a drug company have been found to have followed a female official from the US Food and Drug Administration.

The case has attracted the attention of investigators working for Senate Finance Committee Chairman Max Baucus, who has described the action as outrageous.

The drug company, Amphastar Pharmaceuticals, allegedly paid more than $100,000 to New York based private investigation firm, Kroll, to unearth details about the FDA official's husband and two daughters.

They even followed her on a business trip to Thailand.

Kroll reportedly managed to access her emails, phone records, voicemails and expense reports.

Amphastar supposedly took the action as it wanted to know whether the FDA official was in favour of it bringing to market a generic prescription drug for blood clots.

The company said it was concerned the official was unfairly favouring a competitor in the drug approval process.