The phrase "dubious legality" means something that is doubtful or uncertain when it comes to following the law. It suggests that there might be legal concerns or questions about the activity or situation in question. Full definition
They now have the capacity to create public disorder through strikes, demonstrations, and illegal actions, and their heavy contributions to political campaigns gives them the capacity to persuade members of a major political party to take actions of dubious legality on their behalf. (educationnext.org)
In Baby Milk Action's assessment, Nestlé's strategy violates the International Code of Marketing of Breastmilk Substitutes and is of dubious legality under UK law (details and images below). (babymilkaction.org)
In 2000, however, the House of Commons Select Committee on Foreign Affairs found that the war was illegal, though it offered by way of mitigation the conclusion that: «NATO's military action, if of dubious legality in the current state of international law, was justified on moral grounds.» (newlawjournal.co.uk)