Interest-tax authority designation: income-tax authorities perform interest-tax functions with aligned jurisdiction and Board oversight. Defines interest-tax authorities as the income-tax authorities listed in the Income-tax Act, requiring them to exercise interest-tax powers over persons within their jurisdiction, with jurisdiction consonant with that under the Income-tax Act and linked to business location for certain credit institutions. Officers must follow Board directions, subject to prohibitions on directing particular assessments or interfering with the discretion of the Commissioner (Appeals), and supervisory guidance is to be followed from specified senior income-tax officials; Section 118 provisions apply unless the Board notifies otherwise.