The UK industry argues that the directive, set to enter into force in August, will see around 270 nutrients currently included in supplements removed from the market and significant damage to UK trade.
Two parallel cases against the European Commission will be heard at the European Court of Justice tomorrow -one from the National Association of Health Stores and Health Food Manufacturers' Association, that seeks to undermine the legality of the directive, and another brought by health campaign group the Alliance for Natural Health (ANH).
The ANH is hoping that the judges will allow for national derogation from the directive, so that certain products can remain on markets under separate national regulations.
The results from tomorrow's hearing will not be known until some months later.
The Conservative party is also set to take up the fight in a House of Commons debate tomorrow afternoon.