I think this is discriminatory on the basis of faith and/or ethnicity. Most of the analogies used to justify this are miles off target: wearing a niqab is not the same as other sorts of face-coverings: people who wear them have deeply held beliefs that lead them to do so. There's no reason that it should present any problems whatsoever in going into a bar, restaurant or wherever.
However I also entirely believe it should be for the business owner to set the rules of his establishment. If he wants to discriminate on faith, race or culture, that's really his call. I don't see any particularly good reason why it should be otherwise.
In short, **** 'em all - I don't care.