What does a bar being 会員制 (members only) mean?

Though bars like this have been steadily declining in number since the end of Japan's bubble era, you may still run across a few while walking through the city (especially Ginza). As the name indicates, members-only bars require you to be a member yourself or be the guest of a member. Usually you'll be required to pay some kind of registration fee in addition to yearly membership dues for the privilege of drinking at that particular bar.