"The working of the proposed amendment is such that it would give wide discretionary powers in this regard," Modi, who is also state's Finance minister, said in his letter to Union Finance Minister P Chidambaram.
He said that the state government earns revenues from PSUs and Beverage Corporation (set up by the state government) to run wholesale business of liquor) by imposing privilege fee.
"The proposed amendment amounts to imposition of tax on state government income and therefore violates Article 289 of the Constitution," he said in his letter dated April 25.
Modi is chairman of empowered group of ministers on GST.
He urged Chidambaram that an official amendment be moved in the current session of Parliament to drop this proposed amendment contained in clause 7 of the Finance Bill, 2013.