Do not use brackets to enclose parenthetical statements inside other parenthetical statements. Rewrite the sentence to eliminate the need for brackets.
Preferred
Discouraged
To comply with the European Telecommunications Standards Institute (ETSI), the shelves fit either 300 mm bays or 600 mm bays.
The shelves fit either 300 mm bays or 600 mm bays (to comply with the European Telecommunications Standards Institute [ETSI]).
