Chinese regulators yesterday issued a public ultimatum to Microsoft after questioning a senior executive of the company, signalling authorities are resorting to increasingly tough tactics to win antitrust cases against foreign companies.

The State Administration for Industry and Commerce posted a notice on its website yesterday stating Microsoft had 20 days to answer queries on “incompatibility issues” with its Windows operating system, after an interview with vice-president David Chen. Antitrust lawyers said the aggressive public tone may mean the government is unhappy with the US group’s behaviour. Microsoft reiterated it was “serious about complying with China’s laws and committed to addressing the SAIC’s concerns”.

But Wei Shilin, of the Beijing Competition and Anti-Monopoly Law Commission, a non-governmental body, said the SAIC was using unprecedented tough rhetoric. “Previously, the SAIC has been more discreet,” he said, which he interpreted as either a change to more transparent and legalistic behaviour, or “there is some dissatisfaction about Microsoft’s attitude”.