Human rights lawyer Anon Nampa, a core member of the Resistant Citizen Group, posted a message on Facebook on Tuesday calling for supporters to rally in white at the Victory Monument at 6pm if former commerce minister Watana Muangsook was not released.
He said the Resistant Citizen Group invited all of those who disagreed with the National Council for Peace and Order's (NCPO) detention of Mr Watana to gather at the Victory Monument at 6pm if the Pheu Thai politician was not set free by the military by noon today.
Mr Anon explicitly asked those intending to join the rally to wear white clothing.
Deputy Prime Minister Prawit Wongsuwon told reporters the rally would not be allowed. Mr Watana had been "invited" to meet the military because he had breached an agreement made with the NCPO.
Mr Wattana reported to the NCPO at the 11th Army Circle at 11am on Monday, and was escorted away by soldiers. He was summoned after he continued posting remarks on Facebook criticising and opposing the draft constitution, which will be put to a public referendum on Aug 7.
It was not known where he was being held.
Gen Prawit said people should not worry about Mr Watana because all was still well with him. Mr Watana had been asked many times to refrain from making comments at this time and to allow the government and the NCPO to get on with their job, but he did not heed the warning.
Asked whether Mr Watana would now be sent to a special week-long re-education camp arranged by the NCPO, Gen Prawit said this would be decided by people responsible for handling this matter, not by him.
In response to criticism by international human rights organisations over the way the NCPO is exercising its power, Gen Prawit said:
"We have not infringed on anybody's rights. We have only asked for cooperation regarding the expression of opinions, as we are the holders of state power. We have clearly declared there will be a general election in 2017. We are now in the process of holding a public referendum on the draft charter."
Gen Prawit said he was confident the matter would not escalate and trigger unrest, and that the situation would be remain control during the lead up to the referendum.