The company suspended trading in early March on the Singapore exchange while it seeks out an "independent" review to clarify its dealings in Myanmar to investors.

ETC declined interview requests, and Myanmar's embassy in Singapore didn't respond to requests for comment.

The row over the development is a reflection of the fragmented international response to the 1 February coup. Activists might cause headaches for ETC, but the company can't be in breach of sanctions because Singapore hasn't imposed any.

Both critics and proponents of a tougher approach agree that up until now the sanctions - which only targeted Myanmar's top brass - have been fairly weak.

"The Myanmar military are not going to fall down on the floor, cry and say 'oh my god, I've lost my visa to the US, my life is over'. They'll probably laugh," said Kishore Mahbubani, a former Singapore diplomat and a Distinguished Fellow at the Asia Research Institute at the National University of Singapore.

More broadly, sanctions as a policy tool have a patchy record.

Researchers from the Peterson Institute for International Economics (PIIE) evaluated over 200 cases and found that only a third were a complete or partial success. Others using the same data put the hit rate at just 5%, arguing the PIIE researchers were too generous in their definition of success.

Their track record in Myanmar - which was not part of the PIIE study - is hotly debated.

Some say they played a key role in forcing the military regime to release Aung San Suu Kyi and reopen the country a decade ago, while others say they either weren't significant or only made a difference after the ruling junta decided to change course.

Gary Hufbauer, who led the PIIE's research, said sanctions tend to have a higher chance of success against poor countries like Myanmar.

But they tend to be most successful when the goals are modest, the target countries are not autocratic, and they lack external "black knights" who might throw their economy a lifeline.

Previous sanctions on Myanmar have had a humanitarian impact. For example, the US state department estimated that a 2003 US ban on Burmese textile imports cost 50-60,000 jobs (although orders from the EU mitigated the effect).

Mr Horsey worries that ordinary people rather than the government could again pay the price, especially if the sanctions turn into a broader attempt to bankrupt the state. But human rights groups say the current sanctions are more targeted than those Myanmar faced previously, and point out that democracy activists in Myanmar are themselves boycotting military-linked companies.

"We're not doing anything that the Myanmar people aren't doing themselves," said Phil Robertson of Human Rights Watch.

If sanctions are aimed at hurting the military without shutting down the economy, the question then becomes whether or not foreign businesses can still operate in Myanmar while tiptoeing around the two conglomerates.

Htwe Htwe Thein, an Associate Professor of International Business at Curtin University in Perth, said the two businesses are not all-encompassing, and many consumer goods companies could probably continue to operate. But the same isn't true for Myanmar's resources sector.

"The ownership of the military is rampant in there. It's everywhere in the extractive sector," she said.

But if sanctions force western oil and gas companies to withdraw, Mr Horsey expects that businesses from China or Thailand would replace them.

"If companies like Woodside and Total are forced to divest, they're going to have to sell off their assets rather cheaply, and it's pretty obvious who's going to buy them up," said Mr Horsey.

China and Thailand account for more than half of the country's trade volume, while Singapore is the single largest foreign investor, generating $11bn over the past five years according to Myanmar government figures.

While the Association of Southeast Asian Nations (Asean) has called for a peaceful resolution to the crisis, the group has flatly rejected sanctions.

Mr Mahbubani argues that quiet diplomacy behind the scenes could accomplish more.

"It's the southeast Asian way of avoiding confrontation. And frankly, you have to acknowledge that has kept Southeast Asia at peace for 30, 40 years now, finding diplomatic solutions, talking to each other and changing people's minds," he said.

Phil Robertson attributes Asean's reluctance to self-interest.

"If it was left to Asean, nothing would happen at all," he said.

"And the idea that they're somehow going to be part of the solution is rather laughable".

Mr Mahbubani sees it very differently. He thinks the west's brash, critical approach during the Rohingya crisis, loudly condemning Aung San Suu Kyi for her reluctance to act, may have convinced the military that they could move against her because she no longer had allies. And he thinks it's unlikely that sanctions will change their mind now.

"They are very stubborn people. The more public pressure you put on them, the more they'll dig their heels in," he said.