What is the ruling on a husband preventing his wife from wearing the niqab if she is already wearing the hijab, and is it permissible to prevent it if the niqab might cause harm to the couple from government authorities?

Covering the face is obligatory according to the more preponderant opinion, and it is not permissible to uncover it except in cases of proven or highly probable necessity, not merely imagined necessity, based on the hadith "There should be no harm nor reciprocating harm." A woman should minimize her outings if she is compelled to uncover her face.