Is a husband's choice of a second wife—despite his mother's strong objection and severe displeasure—considered disobedience to parents?

Polygyny is permissible for those who are able to be just, and it does not require the consent of the wife or her mother. There is no sin upon you if your mother becomes angry because you agreed to the marriage; for obedience to parents has its legitimate bounds. Strive to conciliate your mother and gain her pleasure.