The ethnic Madhesi minority in the south of the country rejected the constitution, saying new federal states marginalized them by splitting their homeland. (Getty)
Two political parties left Nepal's ruling coalition on Sunday, deserting the fractious alliance ahead of a vote of no-confidence that Prime Minister K.P. Oli looks likely to lose.
The no-confidence motion, lodged by former Maoist rebels who installed Oli in October but fell out with him after accusing him of failing to honour a power-sharing deal, is due to be put to a vote in the 595-member parliament later on Sunday.
Nepal has been plagued by turmoil for years and the latest uncertainty over Oli's fate risks the further sapping of business confidence.
"We were left with no alternative because of the arrogance of the prime minister and his party," Kiran Giri, a senior official of the Rastriya Prajatantra Party (RPP) told Reuters, referring to party's decision to abandon Oli's coalition.
The Madhesi Janadhikar Forum Nepal (Democratic) is the other party that said it was leaving the alliance.
Both parties said they would join the opposition in Sunday's vote aimed at toppling the Himalayan country's 23rd government since multi-party democracy was introduced in 1990 after bloody protests.
Oli was not available for comment but aides said he would respond to opposition accusations in Parliament.
Nepal's neighbours, China and India, jostle for influence over the volatile young republic and are concerned that prolonged political paralysis could turn one of the world's poorest countries into a haven for criminal gangs and militants.
Nepal has been flirting with crisis since September when it adopted its first republican constitution.
The ethnic Madhesi minority in the south of the country rejected the constitution, saying new federal states marginalized them by splitting their homeland.
The Maoists called off a bid to oust Oli two months ago after he said he would address the Madhesi concerns and rebuild homes destroyed in earthquakes last year.
But Oli's critics said he did not do as he promised.
"The Prime Minister became ego-centric and self-centred, refusing to listen," Maoist chief Prachanda, said in parliament on Friday. "This made us unable to continue to work with him."
Prachanda, who goes by his war nom-de-guerre meaning "Fierce", is the favourite to replace the 64-year-old Oli.
Minority Madhesis blocked border trade points with India for four months to demand the redrawing of provincial borders and a fair say in government.
They ended the blockade in February after more than 50 people were killed in clashes with police and widespread criticism of the protest that choked off supplies of vital imports from India, including fuel.