retorsion

n.
An act perpetrated by one nation upon another in retaliation or reprisal for a similar act perpetrated by the other nation.

[Probably French rétorsion, from Latin retortus (influenced by Late Latin torsiō, a twisting, wringing), past participle of retorquēre, to cast back. See retort¹.]

This entry contains information applicable to United States law only.

A phrase used in international law to describe retaliatory action taken by one foreign government against another for the stringent or harsh regulation or treatment of its citizens who are within the geographical boundaries of the foreign country.

The typical methods of retorsion are the use of comparably severe measures against citizens of the foreign nation found within the borders of the retaliating nation.