(Bloomberg) -- Teva Pharmaceutical Industries Ltd. is being investigated by the US Federal Trade Commission over patents for certain drugs including asthma inhalers, according to a person familiar with the matter.

The agency is seeking information about contested patents that may have been improperly used to block competition for asthma as well as COPD treatments, the person said.

Teva confirmed it received a civil investigative demand from the agency last week, according to a company spokesperson, who didn’t specify which drugs it involved.

“Teva believes that its patents are properly listed,” spokesperson Kelley Dougherty said, adding its management “continues to stand behind the company’s intellectual property.”

The company’s US depositary receipts fell as much as 3.9% Monday. 

In April, the FTC sent letters to 10 drug companies, including Teva, alleging the companies were improperly using patents to block generic competition as part of a broader challenge against the industry’s practices. Drug manufacturers have been accused of making small changes to drugs in order to keep lower-cost generic versions off the market.

The investigation was first reported by the Washington Post, citing confidential agency documents. 

--With assistance from John Tozzi.

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