If both parties are doing the other a mutual favor, you could call it quid pro quo. It's originally a Latin term, but it's used often enough that you can find it in most English dictionaries. For example, Collins defines it as:
quid pro quo (n.)
1 a reciprocal exchange
2 something given in compensation, esp. an advantage or object given in exchange for another
However, if the one party is retaliating against the other for a perceived injustice, you might consider the term tit for tat, which CDO defines as:
tit for tat (n.)
actions done intentionally to punish other people because they have done something unpleasant to you
It can also be used as an adjective in hypenated form; for example:
The new law for stricter visa requirements is just the latest example in tit-for-tat politics between these two nations.
If you don't like tit-for-tat, there are several alternatives can be found in a thesaurus, such as reprisal or retribution.