Shiv Sena chief Uddhav Thackeray on Friday announced an alliance with Sambhaji Brigade, a prominent Maratha organisation.
The alliance was ideological and forged to uphold the Constitution and regional pride, he said.
The development came at a time when the Thackeray-led Sena is still recovering from the impact of Eknath Shinde's rebellion and resultant loss of power in Maharashtra.
Announcing the new tie-up at a press conference in Mumbai, Thackeray also took on his former ally, the Bharatiya Janata Party, saying that "some people" who think that democracy means finishing off regional identity and regional parties are speaking and behaving in uncontrolled manner.
Sambhaji Brigade had hit national headlines in 2004 when its activists were accused of ransacking the Bhandarkar Oriental Research Institute in Pune as part of protests against an objectionable passage in James Laine's biography of King Shivaji.
But the accused in the case were acquitted in 2017.
To a question about the ideological dissonance that might arise in the alliance, Thackeray asked whether the BJP was working according to the ideals of the Rashtriya Swayamsevak Sangh.
Over the last two months, he was being contacted by parties which are ideologically closer to the Sena and also those whose ideology is diametrically opposite, the former chief minister said.
But all these parties think that they should come together to save regional pride and regional parties, Thackeray added.
Talking about the ongoing legal battle between his faction and the rebel Sena MLAs led by chief minister Eknath Shinde in the Supreme Court, Thackeray said the outcome will decide whether there will be democracy or autocracy in the country.
He also announced that he will be touring the state around Dussehra and is currently focusing on building the party organisation.
Manoj Akhare, the chief of Sambhaji Brigade, said the organization formed its political wing in 2016.
The Shiv Sena and Sambhaji Brigade have decided to form a coordination committee for seamless functioning of the alliance, he added.
Reacting to the news, Maharashtra BJP chief Chandrashekhar Bawankule told reporters in Nagpur that as no mainstream party was willing to join hands with Uddhav Thackeray, he was now forging alliance with a party whose candidates could not even save their deposits in the last assembly polls.
