Seoul: Shares in Samsung BioLogics Co Ltd tumbled nearly 20 per cent , losing almost USD 6 billion in value in their biggest daily intra-day fall, after South Korea’s financial watchdog provisionally decided it had breached an accounting rule. The Financial Supervisory Service (FSS) said it had given preliminary notice to contract biotech drug manufacturer Samsung BioLogics, an affiliate of technology giant Samsung Electronics, and its auditors of measures it could take concerning the provisional breach. Samsung BioLogics said in a regulatory filing on Wednesday that it would prove its books were sound. But its shares fell as much as 19.8 per cent to their lowest since late January, before paring losses to trade down 14.5 per cent. Even then, it was Samsung BioLogics’ biggest intra-day drop since its listing in late 2016. The benchmark KOSPI was down 0.3 per cent. The FSS said it had begun an investigation into the company as an activist group questioned last year whether the company had breached accounting rules to inflate its net profit before its listing. The country’s top financial regulator, the Financial Services Commission, will convene meetings to deliberate on the matter before announcing final measures. Samsung BioLogics reported a 1.9 trillion won (USD 1.77 billion) net profit in 2015, compared to a roughly 28 billion won net loss in 2014 and a 62.4 billion won net loss in 2013. However, the net profit was not a prerequisite for Samsung BioLogics to list in 2016, as the Korea Exchange had instituted new rules allowing companies with growth potential to list despite a net loss, said Seo Keun-hee, analyst at KB Securities. Shares in Samsung C&T Corp, which held a 43 per cent stake in Samsung BioLogics as of end-2017, also fell more than 5 per cent. Shares of Samsung Elec, which owned a 31.5 per cent stake in Samsung BioLogics as of end-2017, were on a trading halt on Wednesday ahead of a stock split.