President Nursultan Nazarbayev issued a decree rejecting the plan only hours after senators asked him to approve a “people’s initiative” to prolong his tenure until 2020, a proposal that has been criticized by the United States and opposition leaders.

But Parliament could still force through the referendum, seen by the opposition as a ploy to avoid a fair election, should four fifths of its members defy the presidential decree and vote in favor of constitutional change.

Some analysts see the move as an attempt to avert a challenge to the 70-year-old Nazarbayev from members of the political elite, who are nominally loyal to him but could produce a strong alternative candidate for an election.

Nazarbayev, known as “Papa” to many Kazakhs, has overseen more than $150 billion in foreign investment during more than two decades as leader of Kazakhstan, the world’s largest uranium miner and a major exporter of oil, gas and industrial metals.

The former steelworker, who rose to become a member of the Soviet Communist Party politburo, announced in September that he would seek a new term in a 2012 election and that he expected no serious challenge to his continued rule. Kazakhstan has never held an election judged free or fair by international observers.

But momentum has been gathering for a plebiscite to extend Nazarbayev’s rule since a self-styled citizens’ forum first made the proposal in late December. Supporters and opponents expect the referendum could be held as early as March.

The “people’s initiative” said it had gathered 2.6 million signatures by Wednesday, far in excess of the 200,000 required under Kazakh law to trigger a request for a referendum.

The United States has condemned the move as a blow to democracy and called on Kazakhstan, a nation of 16.4 million people, to hold free and fair elections.

Kazakhstan’s upper house of Parliament on Thursday voted unanimously to ask the president to approve the referendum, echoing a call last week by the lower chamber.

Nazarbayev rejected the proposal in a decree dated Jan. 6 and published by official newspaper Kazakhstanskaya Pravda on Friday, Orthodox Christmas Day and a public holiday. In June, he publicly rejected a parliamentary proposal to appoint him ‘Leader of the Nation,’ a status that grants him the power to retain strong influence over society even after he steps down as president. But less than two weeks later, the bill came into law after being signed by the prime minister and the speakers of both houses of parliament.

In 1995, Nazarbayev called and easily won a referendum on extending his term to 2000 from 1996. Nazarbayev’s aide, Yermukhamet Yertysbayev, told Reuters this week that he believed the referendum would be held anyway, as the proposal was supported by the political elite and business interests keen to maintain stability in the country.