When a country purposefully stops trading with another country, usually to bring about some action, it is called:

a. a tariff

c. a quota

b. an embargo

d. a non-tariff barrier

This is called an embargo, especially trade embargo - this is actually the name that is more typically used.

For example, recently the Western Countries imposed embargoes on Russia as a response to its invasion of Crimea - a Peninsula in Ukraine.