Five activists were briefly detained and later let go by police on Saturday after leading 50 people to release balloons with a message calling for fairness in the Aug 7 referendum on the draft constitution.
Police took five members of the Four Regions Slum Network, including leader Nutchanat Thaenthong, to the Hua Mak station after allowing them to continue an activity to send aloft 100 balloons with messages reading "Campaign Not Wrong" at Ramkhamhaeng University.
Police planned to charge the group with staging a political gathering for more than five persons, which is banned by the National Council for Peace and Order (NCPO), but later dropped it and let them go after interrogations at the station.
Ms Nutchanat said she and four colleagues were only questioned by police, and insisted the balloon campaign did not violate any law.
The activity was held inside the university campus and was closely watched by police and soldiers.
The organisers held up a banner with saying "Free and Fair Referendum" before wrapping up the event with the balloon release.
Ms Nutchanat also read out a prepared statement demanding that authorities release 13 students, some of them studying at Ramkhamhaeng, who were detained on June 23 in Samut Prakan while handing out leaflets urging voters to reject the draft charter in the referendum. The students were charged by a military court with violating the Referendum Act and defying the ban on political gatherings of more than five people.
Ramkhamhaeng student Suphat Arsasri also called for freedom for the detained students and for all sides to be allowed to express their views on the charter so that voters could make an informed decision in the Aug 7 vote.
The Referendum Act bans public comments for or against the charter, saying the only messages allowed are those that encourage people to vote. And while people testing the law in the physical world have been detained, those campaigning in the virtual world have not been, so far.
They include Suthep Thaugsuban, the former Democrat Party strongman whose street protests paved the way for the 2014 coup. He has taken to Facebook Live to deliver video messages in support of the charter. That prompted a series of online responses from red shirt leader and charter critic Jatuporn Prompan.
Junta leaders have warned the men about crossing the line but so far no legal action has been taken. However, the red shirts' attempt to set up centres to monitor vote fraud was quickly shut down.