17. Subject to the provisions of any Federal law, trade, commerce, and intercourse among the units shall, if between the citizens of the Federation, be free:

Provided that nothing in this section shall prevent any unit from imposing on goods imported from other units any tax to which similar goods manufactured or produced in that unit are subject, so, however, as not to discriminate between goods so imported and goods so manufactured or produced:

the Federal Parliament from imposing by Act restrictions on the freedom of trade, commerce, and intercourse among the units in the interests of public order, morality, or health or in cases of emergency

Provided further that no preference shall be given by any regulation of trade, commerce, or revenue to one unit over another:

Provided also that nothing in this section shall preclude this Federal Parliament from imposing any Act restrictions on the freedom of trade, commerce, and intercourse among the units in the interests of public order, morality, or health in cases of emergency.