Armenia announced on Thursday that President Serzh Sarkisian approved the constitutional referendum which will take place on December 6 in order to establish a parliamentary republic.
Sarkisian took an action for the change of constitution on Thursday after parliament voting on October 5.
Several separatists had been protesting the changes on constitution for days.
According to planned changes, the president will be elected by parliament rather than public voters. Also the president will keep his chair for seven years instead of five.
Opposition activists say the new amendments are just for show so that Sarkisian can stay in power as the head of the governing Republican Party after his final presidential term ends in 2018.
"We should change not a constitution, but this leadership, which intends to reincarnate itself," said Stepan Demirchyan, a lawmaker from the opposition Armenian National Congress.
"The constitutional draft carries substantial risks that the country will slide into a de facto one-party system," said former president Robert Kocharian on his website.
Sarkisian denied the arguments, saying he did not intend to be in power after his term ends in 2018. Also, the president and other political partners say that such a fundamental improvement would decentralize power and ease democratization of the country.