Sun Pharmaceutical Industries Ltd stock skidded after U.S. regulators warned of standards violations at a key plant in the latest blow to India's generic drug industry. The warning comes barely a month after rival Dr Reddy's Laboratories Ltd was reprimanded by the U.S. Food and Drug Administration for issues including record-keeping at three of its plants. The company said it was working to resolve the FDA's lingering concerns about the Halol plant, disclosed in a statement by Sun Pharma. Analysts and investors say the warnings highlight how even the country's biggest drugmakers are struggling to establish uniform manufacturing standards across their facilities, nearly two years after they set out to revamp their processes. In a conference call, Sun Pharma said it has been implementing remedial actions at the Halol plant since the FDA inspected it in Sept. 2014 and highlighted a series of concerns. India's largest drugmakers have been overhauling processes and procedures since then-industry leader Ranbaxy Laboratories Ltd in 2013 paid $500 million to settle U.S. charges that it falsified data and misled regulators. Since then, the FDA has also significantly scaled up inspections of foreign plants, leading to a series of warnings and import bans on manufacturing plants in India over problems ranging from compromising data to hygiene and repair issues. Some in the Indian pharma industry say standards have become stricter over the past two years, and it has been difficult for companies to keep up. India supplies about 40 percent of the generic and over-the-counter medicines available in the United States. The latest warning increases the risk the FDA may ban imports from the Halol plant altogether, which would hit Sun Pharma's U.S. sales, about 15 percent of which come from the plant in question. Morgan Stanley analysts said in a note they had lowered their estimates for 2017 and 2018 earnings per share, citing expectations of slower U.S. growth due to delays in Sun Pharma getting U.S. approvals to launch products made at Halol.