BANGKOK -- The deadly new coronavirus has struck a thriving business arm of Thailand's powerful military, laying bare what critics call a culture of impunity that has protected these money-spinners from public scrutiny for decades.

Public health officials have fingered the military-owned Lumpinee Boxing Stadium in Bangkok as the source of one of the country's largest clusters of COVID-19 infections -- over 50 out of the 1,388 cases reported as of last weekend across Thailand. Officials fear there could be up to 130 new infections from this cluster based on the people who have the virus after coming into contact with spectators infected at the event.

The infections were traced to a tournament of Muay Thai, or Thai-style boxing, held on March 6 at the stadium, defying a request by the Sports Authority of Thailand three days earlier to cancel the event on the grounds of containing the outbreak.

"There were about 5,000 spectators from different parts of the country at the stadium that night," wrote an incensed Veera Prateepchaikul, a conservative-leaning columnist, in the English-language daily Bangkok Post on Monday. "The damage is devastating."

Military intelligence and political sources say that the 11 boxing bouts that day were intended partly to raise funds for the military cadet class that Gen. Apirat Kongsompong, the army commander, hails from. The attendees included a who's who of the country's political and entertainment elite, top military brass and executives of companies that the military's business arms trade with.

There is alarm within Prime Minister Prayuth Chan-ocha's government that the leaders of the military -- the most powerful pillar propping up the government -- may be exposed to the pandemic. The concerns are understandable, say military intelligence sources, after reports that Gen. Natapol Nokpanit, the deputy commander-in-chief of the army, was listed among one of the 50 infected in the boxing stadium cluster. He belongs to the quintet of the most powerful generals in the country, headed by Gen. Apirat, and dubbed the "Five Tigers."

Spectators wear face masks while watching a Muay Thai match at Rajadamnern Stadium in Bangkok, Thailand on March 12.

Other high-profile COVID-19 patients receiving care are Maj. Gen. Rachit Arunrangsi, head of the army's welfare department, who runs the Lumpinee stadium, and Matthew Deane Chanthavanij, a Thai television celebrity. Those tested after attending the boxing bouts include a political ally of the regime in the appointed Senate and a junior member of the cabinet.

The spotlight on the Thai military's commercial ties comes on the heels of the harsher exposure in February of the sprawling network of businesses the army has a stake in but which are not subject to public scrutiny.

According to Surachart Bamrungsuk, a respected Thai national security scholar, the Royal Thai Army draws income from 15 types of commercial ventures. They include two television stations, 126 radio stations, 100 gas stations and over 30 golf courses. In addition, the military indirectly operates horse-racing tracks, shooting ranges, restaurants, road construction ventures, convenience stores, flea markets and boxing stadiums.

This business empire came under public scrutiny after a national tragedy in February, when a sergeant major went on a shooting spree, killing 29 people in the northeastern city of Nakhon Ratchasima, commonly called Korat. This, the country's worst mass shooting, was triggered by a land deal gone wrong with an estimated value of $13,000. The assailant's victims included his commanding officer, a colonel, who was involved in a side business to provide housing -- a common practice between high-ranking officers and their subordinates in military camps across the country.

The military's link with this shady business put the Prayuth government in an awkward position, since the prime minister himself is a former army chief who led a 2014 coup and the military junta that ruled until elections last March. That was the country's 13th successful putsch since its absolute monarchy ended in 1932.

To contain the damage -- and uphold the military's privileged status as a "sacred organization" -- Apirat rushed to strike a deal with the regime as part of a promised business reform plan. Under it, the military's private ventures will be handed over to the Finance Ministry for management by May.

But senior military veterans questioned this apparent face-saving effort to limit the damage to the multibillion baht, off-the-books enterprises. These businesses are rooted in decades of privilege and their earnings lubricate military culture from top brass down.

"It is not easy to clear these billions of baht of cash flow overnight," a retired general told the Nikkei Asian Review. "There will be a backlash from within the army since many military units and top brass benefit from the money that helps with welfare, even covering funeral expenses." One billion baht equals $31 million at current rates.

That was evident two months before the February shooting, when the military stood its ground to protect its business privileges. It happened during an attempt in parliament to pry open details of around 19 billion baht ($582 million) in unexplained funds in the current defense budget.

Opposition parliamentarians sought clarity on the amount, which was included as part of the 233.3 billion baht defense budget estimate. Defense accounts for about 7% of the 3.2 trillion baht national budget for the 2020 fiscal year.

"The 18.6 billion baht was an unknown amount. No one knows where the money would come from nor what it would be used for," said Thanathorn Juangroongruangkit, an outspoken opposition leader who has since lost his seat in the legislature and whose Future Forward Party was dissolved by a controversial Constitutional Court ruling.

"There was no transparency and no audits available," Thanathorn said of the military accounts.

Deputy Prime Minister Prawit Wongsuwan, a staunch military and political ally of Prayuth's, deflected such criticism. After that December challenge from Thanathorn, Prawit said the money was for the military's welfare activities.

But the coronavirus outbreak has weakened the foundations of the military's protected business.

"Trying to reform the army business 'just for show' will not work this time," said a military intelligence source. "The military's reputation is taking a beating because of these shady businesses functioning like they are untouchable."