(Adds potential financial impact)
MUMBAI, May 23 (Reuters) - The U.S. Food and Drug Administration imposed an "import alert" on a plant operated by generic drugmaker India's Wockhardt Ltd, sending its shares down 20 percent on Thursday to their lowest level in seven months.
An "import alert", effectively a ban, results in detention without physical examination of drugs from firms that have not met so-called good manufacturing practices, according to the FDA website.
Wockhardt said that the FDA's action potentially affects $100 million in revenue on an annualised basis, but said it should be able to restore most of that within 6 to 9 months by shifting production to other facilities.
The company generated revenue of $908 million in the fiscal year that ended in March 2012.
Wockhardt Chairman Habil Khorakiwala said the $100 million figure was a "worst-case scenario," and said it was not clear how long the ban would be in place.
"We have to interact with the FDA and deal with those issues," he said on a conference call with reporters.
"We are making all kinds of effort to satisfy FDA with the GMP (good manufacturing practices) compliance in that particular facility," he said.
In April, Wockhardt said that the FDA had carried out an inspection at its injectables plant in Aurangabad in western India, and had issued form 483s to the company. A form 483 is issued when inspectors see conditions that they believe may violate U.S. rules, according to the FDA.
The company's shares fell 20 percent, their daily limit, to close at 1,313.80 rupees in a Mumbai market that dropped 2.1 percent. (Reporting by Tony Munroe and Sumeet Chatterjee, editing by William Hardy)