Malaysians will go to the polls next month, officials announced on Tuesday, with the long-ruling and scandal-tainted ruling coalition facing one of its toughest ever challenges from veteran ex-leader Mahathir Mohamad.

Prime Minister Najib Razak’s Barisan Nasional (BN) coalition, which has been in power for six decades, has seen its popularity wane in recent years, a slide further compounded by a multibillion-dollar scandal surrounding state fund 1MDB.

Najib is still tipped to win due to BN’s firm grip on Malaysia’s weakened institutions, and what critics claim are efforts by the government to rig the election through gerrymandering and other forms of cheating.

But he faces a tough challenge from Mahathir, 92, who was Malaysian premier for over two decades but has come out of retirement to take on his former protege Najib at the head of the opposition.

The poll date announced by the election commission – May 9 – sparked fury among the opposition who claimed a weekday election was deliberately chosen to keep turnout low, favouring Najib.

It is the first time in almost 20 years that a Malaysian election has been set for a weekday.

“I am very, very angry,” opposition candidate Maria Chin Abdullah said. “This move by the election commission is obviously to ensure victory for the ruling party.”

Najib is under pressure from allies in his United Malays National Organisation (UMNO), the main coalition party, to score an emphatic victory after the government lost the popular vote in at the last election in 2013.

Voters had become increasingly disillusioned over recurring graft scandals, divisive racial politics in the multi-ethnic country, and the rising cost of living.

Massive financial scandal

The 1MDB scandal has only added to Najib’s woes.

Billions of dollars were allegedly looted from the fund in an audacious campaign of fraud and money-laundering which is being investigated in several countries, and it is claimed that large sums ended up the personal bank accounts of Najib.

Najib, who has been prime minister since 2009, and the fund deny any wrongdoing.

The 64-year-old has so far weathered the scandal by sacking critics in government and launching a crackdown that has seen opponents arrested on various charges.

His prospects at the election have been helped by a robust domestic economy while he has vowed to protect the country’s Muslim majority, a key vote bank for BN.

As the polls approached, the government has taken steps critics say are desperate efforts to cling on to power – the BN-dominated parliament voted to redraw constituency boundaries in a manner analysts say favours the ruling coalition.

MPs also voted in favour of a law banning “fake news” that could see offenders jailed for up to six years, which some fear could be used to crack down on dissent.

Victory is however less certain due to the comeback of Mahathir.

In a stunning volte-face, he was named the prime ministerial candidate in the opposition coalition Pact of Hope, which is filled with parties he crushed during his time in power.

Mahathir has long championed the Malay cause and the opposition hopes he can win over Muslim voters disillusioned with BN, to bolster their support base of urban voters and ethnic minorities, particularly the Chinese.

The government lost a two-thirds parliamentary majority, needed to amend the constitution, in the 222-seat parliament at the 2008 election and is hoping to win it back.