The Congress is attending the 'Save the Constitution' march; West Bengal Chief Minister Mamata Banerjee is sending a senior leader from her Trinamool Congress and a number of other opposition parties have confirmed participation.
Four days later, on January 30, the action moves to Delhi, where again opposition parties will meet at the base of the Mahatma Gandhi statue in parliament, this time at the invitation of BJP leader Yashwant Sinha. Another BJP leader Shatrughan Sinha -- who like Mr Sinha is counted as a rebel for his frequent criticism of the party and the government it leads at the centre -- is expected to be there.
Mr Sinha's new platform is called the Rashtriya Manch, officially an apolitical forum drawing people from across parties to discuss important national issues. Former union minister Dinesh Trivedi is Mamata Banerjee's representative at both meetings. The Congress is likely to send Ashok Pradhan to Mumbai and Manish Tiwari to the Delhi meet.
Pawan Verma of the Janata Dal United will attend the Delhi rally, as will senior retired ambassadors and bureaucrats.
The Congress's participation in the Mumbai march has also led to speculation on the party renewing its partnership with the NCP ahead of the assembly elections in Maharashtra, due next year too. The Congress and NCP together governed Maharashtra for 10 years before losing power to the BJP and Shiv Sena in 2014. A period of estrangement has followed in which Sharad Pawar was seen getting close to the BJP.
This comes as the Shiv Sena has announced an end to its alliance with the BJP, asserting that it will contest both the national and state elections alone next year.
"The BJP is diluting the meaning of the constitution and this is why we are taking out this march," said former Maharashtra Chief Minister and Congress leader Ashok Chawan.
Other parties that have said they will participate in the march are Tamil Nadu's main opposition party the DMK, and Uttar Pradesh heavyweights the Samajwadi Party and the Bahujan Samaj Party.