The number was a significant drop from the 68 violations handed out during a similar effort this time last year.
Operation Back to School sent four undercover ALE agents and several uniformed Chapel Hill police officers to local grocery stores, convenience marts and bars to apprehend minors attempting to purchase or consume alcohol.
ALE Agent William Stanley said this year's operation, which lasted all weekend, indicated that efforts to curb underage drinking in the last year have been successful.
"This is a big reduction from last year, which hopefully shows that the training and word is getting out that this is just not acceptable to society," Stanley said. "We love to go out and see that people are complying with the law."
Among the 20 citations given this weekend, one of the largest busts in terms of quantity of alcohol seized involved Gregory Wilson of 230 Granville Towers East.
Wilson, a UNC sophomore, was charged with one misdemeanor count of obtaining alcohol with a fictitious ID and one misdemeanor count of aiding and abetting another minor.
Agents seized three cases of Budweiser and two 12-packs of Busch Light from Wilson at 12:10 a.m. Monday in the Granville Towers parking lot.
Wilson refused to comment on the charges.
Jeremy Kidd, 21, of Pittsboro was also checked for identification by Stanley early Monday morning. Kidd was stopped in the Granville Towers parking lot en route to Fraternity Court with a six-pack of Miller Lite.