The letter said political conflict had emerged across the country because of Prayut's failure to impose reforms to tackle corruption, the economy and other aspects of governance.
It also said that the number of Covid-19 infections in Thailand had soared to over 2,000 per day because of the Prayut government's failure in procuring and managing vaccines.
To resolve the country’s crisis, the power of government and the private sector would have to be combined and Prayut would have to resign, it added.