The five independent experts, appointed by the Geneva-based U.N. Human Rights Council, say the conservative Polish government must ensure there is "meaningful civic space" at the Dec. 3-14 talks in Poland's southern city of Katowice.
The group said new laws appear to give Polish security agencies sweeping powers to put participants at the talks under surveillance currently reserved for suspected criminals. They said another Polish law could prevent the kind of spontaneous protests that are a staple of the annual U.N. climate talks.
Polish officials didn't immediately respond to a request for comment, but in the past have said the law would not limit freedom of assembly.
In January, the then-deputy environment minister, Pawel Salek said preventing spontaneous demonstrations was necessary to ensure security in an age of terrorism. He said anyone who wants to can organize a demonstration but must register it ahead of time.