A billionaire Thai opposition figure was charged Tuesday with defaming the monarchy after he questioned the government's alleged over-reliance on coronavirus vaccines from a company linked to the royal family.

Thanathorn Juangroongruangkit, founder of the now-dissolved Future Forward Party, posted a video on Facebook in January in which he queried whether Thailand was leaning too heavily on Siam Bioscience for its vaccination campaign.

The company is owned by the Crown Property Bureau, which manages the royal family's multi-billion-dollar fortune.

Police on Tuesday charged Thanathorn with lese majeste and a computer crime over the video, but he was defiant.

"It has had a positive result -- encouraging the government to reassess the vaccine policy to manage the Covid-19 situation. There is nothing to worry about," he said after being charged.

"(The police) did not bring up any quotes or anything that was said specifically. It was generally a charge for speaking via Facebook."

Those convicted under Thailand's strict royal defamation laws can face up to 15 years in jail per charge.

Thailand has ordered 61 million doses of the AstraZeneca vaccine. Siam Bioscience plans to manufacture 200 million doses of that vaccine for the kingdom and wider region each year.

Thanathorn's will have to report to police again on May 7.

Before it was disbanded, his Future Forward Party was Thailand's third-largest, drawing millions of supporters who were attracted to his anti-establishment platform during the 2019 election.

But they were felled by swift legal action, which saw its top executives, including Thanathorn, banned from politics and the party dissolved.

More than 70 people are currently facing royal defamation charges in Thailand including prominent student leaders who kicked off a youth-led pro-democracy movement last July.

Its demonstrations last year attracted tens of thousands at their peak but the movement has slowed in recent months due to a new wave of coronavirus cases.

Police used rubber bullets and water cannon to break up a demonstration outside Bangkok's Grand Palace on March 20.

The protests have called for the resignation of Prime Minister Prayut Chan-O-Cha's government and a rewrite of the military-scripted constitution.

But the most controversial demands have been for reforms to the monarchy, including the abolition of the royal defamation laws.