The Garage, in Sauchiehall Street, Glasgow, carried an advert on its website offering a trip to New York as a prize in a draw in which entry involved buying a Smirnoff Gold or Applebite Gold from the bar.
The ad stated a gamecard for the draw was on offer with every Smirnoff Gold or Applebite Gold bought. Participants could enter as many times as they wished by buying more drinks and submitting more gamecards.
A complaint was also lodged two adverts for competitions that required a 'like and share' on the Garage's Facebook page resulted in the advertising of alcohol to those under 18.
The first featured a contest to win a 'VIP Jagermeister night out' and a second featured an image of a bottle of spirits and four glasses with the prize of a VIP booth and a bottle of vodka.
The Advertising Standards Authority (ASA) upheld the complaints, saying competition to win a trip to New York "encouraged participants to purchase, and consume, a number of drinks to improve their chances of winning".
It added: "We concluded the promotion therefore condoned and encouraged excessive consumption of alcohol."
The ASA said that when posting content on Facebook advertisers were able to restrict content so only users registered as over 18 were able to see it.
The body said it understood that such age restrictions applied to the original post as well as re-posts, which resulted from 'likes' and 'shares'.
But the ASA said representatives for the Garage had chosen not to use that method of ensuring the ads were not seen by any Facebook users under 18.
"Because Beachcove (the Garage owners) had had the ability, through the selection of media and the context in which the ads appeared, to prevent the ads being directed at people under 18, but had failed to do so, we concluded the ads were in breach of the Code," said the ASA.
The body also upheld a complaint that a separate Facebook advert for a Tuesday night event featuring a drinks promotion included an image of three young women who appeared to be under 25, in breach of the Committee of Advertising Practice code.
Beachcove Ltd was told by the ASA the adverts must not appear again in their current form.
Beachcove provided a copy of a poster that also promoted the 'trip to New York' draw and highlighted it had the drinkaware logo on and therefore considered the promotion did not therefore encourage excessive consumption of alcohol.
Officials said staff were trained to monitor customers for excessive drinking, so customers would not be able to abuse the promotion.
The company also said it did not have control over who the Facebook ads were shared with beyond those people who had liked the page. The firm said its focus was in marketing the venue to people aged 18 to 25, which was their main customer base.
It provided statistics from a social media analytical tool that indicated 3% of the people who had liked the page were under 18. It said that was because that in addition to its nightclub nights, the Garage hosted live music events, which, under the terms of its licence, children of 14 and over could attend.