How are administrative agencies kept in check by the government?
In theory, by the Congressional Review Act, which authorizes
Congress to review any administrative rule (but it has been used
only once). Also, any administrative rule has to be based on and in
substantial conformance with the law. Finally, in general, rules of
administrative agencies and the decisions that are based on them
are reviewable in court (to obtain such review, one has to show
that one has been personally harmed by such decision/rule).