They are Banharn Silpa-archa, chief adviser of the Chartthaipattana Party, Chuwit Kamolvisit, leader of the Rak Thailand Party, and Ukrit Mongkolnavin, chairman of the independent National Rule of Law Commission (NRLC).
They were among a group of 16 people ordered last night to report to the NCPO today between 10am and 12 noon.
Thitima Chaisaeng, a former Pheu Thai MP, who was among the 114 people ordered to report to the coup makers under an order issued on May 24, also turned up at the army auditorium.
The NCPO on Monday night also issued an order for those who were required to report to it under previous orders but had not done so must report by the 12 noon deadline today, or face a maximum jail term of two years and/or a fine of 40,000 baht.
They would also be banned from making any financial or property transactions.