India won’t allow commercial flights to operate until it is confident that the coronavirus outbreak is under control, the aviation minister said, piling further pressure on the country’s cash-strapped airlines.

The ban will be lifted only when the government determines that the virus is no longer a threat, Hardeep Singh Puri wrote in a Twitter post. Airlines had been selling tickets in advance even though the government said there’d been no decision on allowing them to operate, Puri wrote in a series of tweets. Airlines will be given “sufficient notice and time” to resume flights, he said.

A regulatory order banning ticket sales, which applies to local and foreign airlines, means carriers will likely have to take more steps to reduce costs having already put some staff on leave without pay and reducing salaries. Airlines use funds from advance ticket sales to cover day-to-day expenses.

Shares of InterGlobe Aviation Ltd., which operates the nation’s biggest airline IndiGo, fell as much as 5.8% Monday in Mumbai. Smaller rival SpiceJet Ltd. slid more than 1%.

India initially announced a 21-day lockdown until April 14, and airlines had started selling tickets before the extension to May 3 was announced last Tuesday. Most carriers have been offering credit instead of refunds if flights are canceled, a practice that other airlines around the world are also using.

The travel restrictions mean the three months ending June 30 will be “virtual washout” for the Indian aviation industry, CAPA Centre for Aviation said earlier this month. Local airlines, some of the world’s biggest customers for Airbus SE and Boeing Co., are likely to defer taking delivery of 200 new planes by as long as two years, according to CAPA.