@Riemann is right - it’s judicial review.
The thing is, it’s not a “personal” discretionary power, like you or I might have in handling our affairs.
It’s the exercise of a statutory power, and the general principle under the common law is that there is no such thing as an unreviewable statutory power. As a matter of the rule of law, any time an official exercises a legal power, there must be some minimal power in the courts to review that decision.
The extent of the court’s power to review will vary from jurisdiction to jurisdiction and in relation to the subject matter. Traditionally, courts give considerable deference to decisions as to who can be allowed into the country, and on what terms.