pretext
Definitions
A reason given in justification of a course of action that is not the real reason.
An ostensible or professed purpose; an excuse.
Examples
He used a minor technicality as a pretext to fire his assistant.
Under the pretext of conducting a routine inspection, the inspector gained access to the restricted area.
She visited the office on the pretext of returning a book, but she really wanted to see if he was there.