Home Minister's office here received three letters in this regard a few days ago, the sources said.
The anonymous letters wanted Chennithala not to continue with the operation Kubera and warned that if it was proceeded he would have to face serious consequences, the sources said.
The crackdown on private money lenders was started a month back after a mass suicide of five members of a family due to debt and threat from henchmen of money lenders.
As part of the operation, a special police team has been formed to carry out raids and seizure of documents of those indulged in illegal money lending business and charge exorbitant interest interest rate for the loan amount they give.
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The sources said along with Kubera, raid against sale of intoxicant products as part of 'clean campus-safe campus' programme might be another reason for the threat letter.
Speaking at an "anti liquor and anti-drug' campaign here, Chennithala had said drug mafia were behind creating communal tension and fundamental activities in the state.