Jurisdiction of income-tax officers

Income-tax officers are required to carry out their duties with regard to the regions, individuals, incomes, income streams, cases, and case types that the Commissioner may specify. When any directives issued under the aforementioned subparagraph assign the same area, the same people, groups of people, incomes, classes of income, cases, or classes of cases to two or more Income-tax Officers, they are each given concurrent jurisdiction and are each required to carry out the aforementioned functions with regard to the aforementioned area, people, groups of people, incomes, classes of income, cases, and classes of cases.

The distribution and allotment of the work to be done may be specified in writing by the Commissioner or the Inspecting Assistant Commissioner designated by him in this regard.

Here is a good article on section 12a.

The Income-tax Officer has jurisdiction over anyone operating a business or practising a profession within the boundaries of the area that has been assigned to him, including anyone residing within the area as well as anyone whose principal place of business or practise is located within the area if they have more than one location where they conduct their business or practise. If a question was raised under this section about whether an Income-tax Officer has the authority to assess a person, the Commissioner will decide it. If the question relates to a region under the purview of more than one Commissioner, the concerned Commissioners will decide it, or if they cannot agree, the Board will.

No one has the right to contest the authority of an income-tax officer after the passage of a month from the date on which he or she filed a return under a section 139 sub-section or after the conclusion of the assessment, whichever comes first, and in the event that no such return was filed, after the time period specified in the notice under section 139 sub-section (2) or section 148 for filing the return has passed.

When an assessee challenges the authority of an income-tax officer, subject to the provisions of the aforementioned sub-section, the income-tax officer, if unsatisfied with the accuracy of the claim, shall refer the matter for perseverance under the aforementioned sub-section before assessment is made. Every income-tax officer shall have all the rights granted by or under this Act to an income-tax officer in respect of any income accruing, originating, or received within the region for which he is assigned, notwithstanding anything stated in the aforementioned section [or section 130A].

The information lies here on the topic 80g income tax.