Move comes as Pheu Thai founder Thaksin Shinawatra prepares to return home after 15 years in self-imposed exile.

The announcement on Monday comes a day ahead of a parliamentary vote for a new prime minister and as Pheu Thai founder and former prime minister, Thaksin Shinawatra, prepares to return to the kingdom after 15 years in self-imposed exile.

Pheu Thai is expected to nominate real estate mogul Srettha Thavisin as the country’s next leader.

The party came second in Thailand’s May 14 election, but took over the formation of government after conservative members of an unelected upper house blocked attempts by Move Forward – the progressive party that won the election – from securing the top job for their candidate.

Srettha, 60, a political newcomer, will need the support of 375 legislators, or more than half the combined upper and lower houses of parliament, to be endorsed as prime minister and form the next government.

Phumtham Wechayachai, Pheu Thai’s deputy leader, told the Reuters news agency that Srettha had the backing of 14 parties, including the United Thai Nation party affiliated with outgoing Prime Minister Prayuth Chan-ocha and the Palang Pracharat party of Deputy Prime Minister Prawit Wongsuwan.

Prayuth, a former general, orchestrated the coup that toppled a Pheu Thai government led by Thaksin’s sister, Yingluck Shinawatra, in 2014.

The Bangkok Post website said the 14-party coalition backing Srettha has 317 votes in the lower house. He will need the backing of an additional 58 legislators to be named prime minister.

Pheu Thai is expected to formally announce the coalition in Bangkok on Monday afternoon.

Move Forward has said it would not back Pheu Thai’s multiparty effort, arguing it distorted the election result and was against the public will.

Opinion surveys show most Thais disagree with Pheu Thai’s plan for a coalition government that includes Prayuth and Prawit’s parties. The poll by the National Institute for Development Administration, published on Sunday, showed that about 64 percent of those surveyed disagreed or totally disagreed with the idea of Pheu Thai allying with the military-backed parties.

Pheu Thai has meanwhile apologised for failing to keep its election pledge of not joining the military parties.

“We have to make adjustments to keep the country going,” said Paetongtarn Shinawatra, who is Thaksin’s daughter.

“Of course, Pheu Thai has the price to pay, that is the criticism of the people. We humbly accept and apologise for making many disappointed and sad.”

She added that Thaksin’s planned return to Thailand on Tuesday had nothing to do with politics.

The 74-year-old former telecommunications tycoon, who was prime minister from 2001 until he was deposed in a 2006 coup, is expected to land at Bangkok’s Don Mueang Airport at 9am (02:00 GMT) on Tuesday. His expected arrival will come just hours before the parliament votes for prime minister.

Thaksin, who has lived mostly in Dubai since fleeing Thailand to avoid a jail sentence for corruption, still faces the possibility of prison time.

“Thaksin’s return on voting day shows that he is confident that Pheu Thai’s prime ministerial candidate will be elected in one round,” said Thanaporn Sriyakul, chair of the Political Science Association at Kasetsart University.