A key regional party in India's ruling coalition has withdrawn its support for the government in protest over a series of economic reforms revealed last week. 

The decision by the Trinamool Congress party from the state of West Bengal, leaves the government of Prime Minister Manmohan Singh weakened and dependent on outside support to pass legislation.

Trinamool is staunchly opposed to the reforms which include allowing in foreign retail giants such as Walmart and Tesco, as well as foreign airlines, and hiking the price of subsidised diesel by 12 per cent.

"Our ministers will go to Delhi to resign. We will not stay in UPA II," Mamata Banerjee, the head of Trinamool, told reporters on Tuesday, referring to the ruling coalition led by the Indian National Congress (INC) party.

Banerjee, who has forced the government into a series of policy U-turns, swept to power in West Bengal in May last year.

"My party's six ministers have decided to resign. It is time to fight the battle alone," she said after a meeting of Trinamool leaders in Kolkata, the capital of West Bengal.

Banerjee added that her party's 19 MPs would not support the coalition but correspondents say the government's parliamentary majority is not at risk.

'No respect'

Banerjee, who said the reforms would hurt the poor, added: "Unfortunately we have not received any respect from Congress despite being their important coalition partner."

Trade unions, backed by the main opposition Bharatiya Janata Party and other regional parties, have called for a nationwide strike on Thursday against the reforms, which have been welcomed by business leaders and investors.

The country's biggest union of truckers announced on Tuesday that it would also join the day of defiance, increasing pressure on Singh and P Chidambaram, his new finance minister, who said reforms were necessary to repair India's strained finances and attract foreign capital and investment.

There has been speculation for months about the possibility of early elections before their scheduled date in 2014 because of tensions in the UPA II coalition.

INC insiders believe they will be able to manage by calling on other regional parties such as the Samajwadi Party or the Bahujan Samaj Party from northern Uttar Pradesh state.