Is a young man's marriage without the consent of his mother, who fears the cessation of his financial support for her and the family, considered an act of disobedience?

Disobeying one's parents is a grave sin, and its reality is every action that causes them significant, not minor, distress, provided that the action is not obligatory. If the action is obligatory, then disobeying the parent in it is not considered an act of disobedience. As for marriage, it may be obligatory, in which case the mother is not to be obeyed, and it is not considered an act of disobedience. However, if it is not obligatory and results in harm to the mother, such as the loss of her financial support, then it is forbidden and considered an act of disobedience.