The Subjunctivisor!
Does luego que require the subjunctive?
It depends. When the main clause is a command or in the (potential) future, luego que requires the subjunctive:
Llámame luego que llegues.
Call me as soon as you arrive.Es importante de llamarme luego que llegues.
It’s important to call me as soon as you arrive.
But luego que takes the indicative when the action in the subordinate clause is either habitual or in the past:
Siempre me llama luego que llega.
He always calls me as soon as he arrives.Me llamó luego que llegó.
He called me as soon as he arrived.