Six regional parties have joined forces to take on the Narendra Modi government and the ruling National Democratic Alliance (NDA) in the winter session of Parliament starting later this month, throwing down a challenge to the ruling coalition.

The development comes less than three weeks before the start of the session, in which the Bharatiya Janata Party (BJP)-led government proposes to take up crucial legislation for debate and passage.

The move could pose more legislative hurdles for the NDA, which is short of a majority in the Rajya Sabha although it has a clear majority in the Lok Sabha. It also gains significance because the Congress party has been unable to secure the post of the leader of the opposition (LoP) in the lower house.

Legislation up for debate and passage in the winter session, which starts on 24 November, include the insurance Bill to raise the ceiling on foreign investment in insurance ventures to 49% from 26%, a constitutional amendment Bill to allow the proposed goods and services tax, amendments to a land acquisition Bill and several labour law changes.

The six are Mulayam Singh Yadav’s Samajwadi Party (SP), Lalu Prasad’s Rashtriya Janata Dal (RJD), the Janata Dal (United) or JDU, Janata Dal (Secular), the Indian National Lok Dal (INLD) and the Samajwadi Janata Party.

Former Bihar chief minister Nitish Kumar, a leader of the JDU, said the six parties would take a united stand in Parliament; he didn’t rule out a future merger of all the Janata parivar (family) parties.

Speaking to the media, Kumar, Bihar’s former chief minister who parted ways with the BJP last year, announced that all the six parties would have a united stand in Parliament even as he did not rule out the merger of all the Janata parivar parties in the future.

“The answer to this (a merger) lies in the future...we can move towards one party," he said. In reply to a question on why the Left parties were not called, Kumar added that political parties “who share our views on certain issues will be contacted. We are open to a dialogue."

To be sure, the parliamentary strength of the six parties is limited. Together, they have 25 members in the 245-member Rajya Sabha and 15 in the 543-member Lok Sabha.

Still, the alliance, if it stays together, may play a crucial role in the assembly elections in Bihar next year and in Uttar Pradesh in 2017 because most of its constituent parties have influence in the two states. The BJP is also eyeing Bihar and Uttar Pradesh, which are ruled by the JDU and SP, respectively. The JDU broke up with the BJP last year.

“It is an old tendency of these parties to come together during crisis. They will together play an important role during elections. It will be tough for the BJP if these parties come together in Rajya Sabha. However, the move may not have much impact with people because the mood in the country is still in favour of Modi," said A.K. Verma, a Kanpur-based political analyst.

PTI contributed to the story.