As LDF made it clear that all roads leading to the Assembly would be blocked, security has been tightened and the entire assembly area cordoned off.
The Finance Minister's office when contacted, said Mani was staying back in the Assembly complex as "priority before him is to present the budget tomorrow".
Besides Mani, some ministers and UDF MLAs are also staying back to express solidarity with the Finance Minister, Congress sources said.
Home Minister Ramesh Chennithala said the government would face the stir sternly if it turns violent.
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LDF claimed thousands of volunteers would take part in the "protest resistance" to be staged outside the Assembly complex.
Aggravating the situation, BJP's youth wing Yuva Morcha has also announced plans to stage dharna before the Assembly.
Earlier in the day, Chief Minister Oommen Chandy took up the challenge of the Opposition, maintaining that the charges against Mani was part of a "political conspiracy" and asserted that the minister himself would present the budget.
Intervening in the debate, 82-year-old Mani had debunked the opposition charges and said his 50-year-long public life was transparent.
Vigilance and Anti-Corruption Bureau had registered a case against Mani in December 2014 in connection with the charges that he had accepted bribe from bar owners to renew liquor licences.
The allegations were levelled by Kerala state Bar Hotel Owner's Association Working President Biju Ramesh.