Is it permissible for me to prevent my husband from traveling to visit his relative in the United States, on the pretext of my disapproval of his travel and his leaving me without financial support, and his staying in a house inhabited by an untrustworthy woman with her brother, especially since I am newly married?

There is no harm in objecting to the husband's travel and refusing to approve it as long as it will leave his wife without financial support, due to the severe warning mentioned concerning those who neglect their families. Examples include the Prophet's (peace and blessings be upon him) saying: "It is enough sin for a man to withhold from those whose sustenance he possesses," and "It is enough sin for a man to neglect those whom he supports." He must spend on his wife what he would spend on his travel. And assuming consent to his travel and the wife remaining without financial support, it is not permissible for him to be in seclusion with a woman who is unlawful for him, based on the Prophet's (peace and blessings be upon him) saying: "No man is alone with a woman except in the presence of a mahram," and his saying: "No man is alone with a woman but Satan is the third of them." Being in seclusion with her is one of the major sins.