Debating the Constitutionality of Section 56(2)(viib) of the Income-tax Act, 1961

I'm firmly on the side of striking down this provision. Section 56(2)(viib) empowers the Government to tax any sum received by an individual from any person resident in a country with which India has an agreement for the avoidance of double taxation if the sum is not chargeable to tax in the hands of such person under the provisions of that agreement or under any other law in force in that country. This provision is draconian and amounts to an unwarranted invasion of the domain of treaty making, an area that is exclusively reserved for the Executive and the Parliament.

The key question is: can the legislature, in furtherance of a policy decision, take away a citizen's treaty right? Can anyone explain to me why this provision was included in the IT Act?