Noting that next general elections were crucial for the Congress, Chavan told reporters here that lot of people are coming together on a common platform to protect the Constitution and democracy.
Alleging that Modi was adopting various strategies to ensure that 'Mahagathbandhan' does not materialise, Chavan said, "Modi's strategy for winning elections will be religious polarisation, massive use of money, and using tactics to make sure that our alliance doesn't materialise."
Asked about BJP leader Ram Madhav's reported statement on the option of ordinance for early construction of Ram temple at Ayodhya, Chavan said they (BJP) have suddenly started thinking of Ram Mandir after four-and-half-years.
"They think they can win by this... their (electoral) promises.. nothing happened and now (they say) build a temple."
"What was this government doing? Why did it not build a consensus among different communities so that an acceptable solution could have been arrived at?" he asked.
Asking people to be cautious over alleged attempts at 'religious polarisation' and the Ayodhya issue ahead of Lok Sabha polls, the Congress leader expressed fears that there could be some attacks on places of worship.
To another query, Chavan said 'unfortunately' under Modi's rule all institutions of democracy have been 'subverted.'
Chavan alleged that Modi was using all investigating agencies against Opposition parties, to browbeat them.
Reacting to Chavan's charges, Telangana BJP spokesperson Krishna Saagar Rao told PTI that 'Mahagathbandhan' was a "failed alliance" and "it is a losers' league".
"It is a survival game.. Inspired by Congress party's dynastic system.. Modiji does not need to scuttle the formation (of grand alliance).. people of India have no interest in this alliance and they will reject it," Rao added.
On the Ram temple issue, Rao said those who were saying that BJP was indulging in polarisation politics were ignorant.
On the charge that Modi was adopting strategies to prevent formation of grand alliance and win elections, Rao said, "BJP doesn't need money or muscle power or polarisation to win polls.
We have proved this time and again in many states... people are electing us because of good governance and relentless focus on the lowest rung of people, farmers and the downtrodden."