79-year-old Htein has been criticizing the military for decades, and after the coup he called for resistance.
"Everyone in the country should oppose those who want to take us back to zero by destroying our government," he said in an interview with the local newspaper Frontier Myanmar shortly after the coup.
Among those arrested are activists, government officials and members of the governing party NLD.
The country's leader Aung San Suu Kyi and President Win Myint were arrested on Monday and are said to be under house arrest.
"Peaceful strike"
Facebook, Instagram and Whatsapp have been blocked in an attempt to prevent protesters from organizing.
Smaller demonstrations have erupted in the cities of Mandalay and Dawai, but no widespread mass protests have taken place.
Instead, several residents show their dissatisfaction with the military by refusing to perform their duties.
Hospital staff at over 70 different hospitals and clinics are on strike, and now some government employees and university teachers have also joined.
- We hope to be able to slow down the entire administration.
It is a peaceful strike, Honey Lwin, a teacher at Yangon University, told Reuters.
On the social media that still works, several protesters are seen holding up three fingers in the air.
The gesture originally comes from the film Hunger Games but has in recent years been used as a symbol against oppression, including during the protests in Thailand.
Wants to arrange a new election
Democracy in Myanmar is both young and unstable.
A military junta ruled the country until 2011, and had been in power for 50 years.
Now the country is once again controlled by the military and Supreme General Min Aung Hliang.
He has long had a major influence on politics in Myanmar, and has been blocked from Twitter, among other things, after he denied that the Muslim minority group Rohingya had been persecuted.
My Aung Hliang has promised to organize a new democratic election because he believes that the country's leader Aung San Suu Kyi won through election fraud.