Malaysian police were moving in by the busload to Merdeka Square in Kuala Lumpur a day ahead of a planned protest in defiance of a government ban.
It's in response to parliament's approval of reforms which opposition-backed campaigners say fall short of guaranteeing fair elections.
Some of the activists already gathering for Saturday's rally are condemning the decision to outlaw it.
SOUNDBITE: 29-YEAR-OLD PROTESTER ARUNA SENA SAYING (English):
"I'm greatly disappointed because I'm a 29-year-old Malaysian, I believe in practicing my human rights but in this country, especially in Malaysia, especially here right now you can see we are not allowed to practice our human rights to assemble, human rights to voice our concern, our freedom of speech."
Organisers are hoping up to 10, 000 will turn out for the rally due to end with a sit-in.
Police fired tear gas and water cannon at a much smaller protest last July.
A big turnout may persuade Prime Minister Najib Razak to consider delaying elections that must take place by April next year.
He's enjoying a popularity boost after announcing social handouts for lower income families and pay rises for civil servants.
Paul Chapman, Reuters
