NEW YORK (Reuters) - Teva Pharmaceutical Industries Ltd. on Friday said Novartis AG's Sandoz unit asked a U.S. court to block Teva's generic versions of Merck & Co.'s Zocor cholesterol treatment.

Sandoz, Novartis' generic unit, has filed a complaint in the U.S. District Court for the District of Columbia seeking approval of its generic Zocor products, Teva said.

Sandoz's legal action could delay the launch of Teva's generic versions of the blockbuster drug, long expected to debut as soon as today, coinciding with the patent expiration on Zocor. Teva has been expected to have exclusive rights on most dosage forms of generic Zocor for as long as 180 days.

Israel-based Teva said the Sandoz unit filed a complaint seeking a temporary injunction to block U.S. regulators from approving generic versions of Zocor, until an appeal can be heard on Sandoz's request to sell its own generic version.

A hearing on the issue is scheduled for Friday morning at 10 am, Teva said.

Piper Jaffray analyst Deborah Knobelman said judges tend to take a few days to weigh such a request, but she expected that Teva would ultimately retain the exclusivity.

"My suspicion is this is only going to be a few-day delay," Knobelman said. "This is just a last-minute attempt to keep Teva from getting its exclusivity period by a competing generic company."

Teva shares fell 12 cents to $31.13 in morning trade on the Nasdaq. The stock had fallen more than 12 percent since Wednesday, after a Merck move to secure preferred health insurance coverage for its branded Zocor raised concern about Teva's market share from its generic.

Though temporary, exclusivity periods can prove lucrative for generic drug companies, especially for blockbuster drugs. Merck reported $3.1 billion in U.S. sales last year from its brand-name Zocor.

Teva said it is eligible to receive exclusivity on 5-, 10-, 20- and 40-milligram strengths of generic Zocor, also known by its scientific name, simvastatin. Indian drug maker Ranbaxy Laboratories Ltd. is expected to have exclusive rights to the 80-milligram version.

Merck also has agreed to authorize Indian drug maker Dr. Reddy's Laboratories Ltd. to sell generic versions of Zocor.

Once generics hit, Merck will see its Zocor sales plummet, as pharmacists begin substituting lower-cost generic copies for the brand. Prescription drugs can lose 80 percent of revenue within months after losing patent protection.

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