on the pretext of; under the guise of
Fixed expression used to indicate that something is done using a stated reason as an excuse or cover. Often followed by a verb phrase describing the real action.
He skipped the meeting on the pretext of work.
I stayed home from school under the pretext of being sick.
From 事 (こと, 'thing, matter') + 寄せて (よせて, the te-form of 寄せる 'to bring near, to attribute'). Literally 'attributing to a thing', it developed into a set phrase meaning 'using something as an excuse'.