New Jersey authorities say nearly 30 bars and restaurants, including 13 TGI Fridays, have been duping customers by filling premium-brand liquor bottles with well-brand alcohol and charging the higher price.

The attorney general's Division of Alcohol Beverage Control said officials on Wednesday seized alcohol and served demands for records at the 29 bars and restaurants targeted during the year-long investigation dubbed "Operation Swill."

Authorities said the bars and restaurants were trying to "fool the customer and increase their profits."

"The customer paid for the premium brand, but was instead, unbeknownst to the customer, poured the non-premium brand," the beverage control office said in a statement.

Officials said more than 100 state investigators worked on the probe, which involved customer complaints and confidential informants. Investigators also secretly took drink samples from the establishments.

Danielle Ferrazzano, a regular customer at Blackthorne restaurant in Parsippany, said she couldn't believe the accusations.

"I see them pour it," she said. "There's my Captain and Coke, whatever it is I drink. I was fine with it. I never suspected anything."

A manager at Blackthorne, who did not want to be named, told NBC 4 New York the allegation wasn't true and that he felt the restaurant was unfairly targeted.

The ABC division would not give specifics on the types of violations that the accused bars and restaurants might receive, but promised that Attorney General Jeffrey Chiesa would announce the details on Thursday.

In general, authorities say ABC has administrative powers against the liquor licenses that bars and restaurants must reapply for each year. Any penalties given by the ABC would be issued against the licenses.

The TGI Fridays accused in the investigation are in West Orange, East Windsor, Old Bridge, North Brunswick, Piscataway, Freehold, Marlboro, Hazlet, East Hanover, Linden, Woodridge, Springfield and Clinton.

The company said in a statement that it "was just made aware of this issue and is working closely with the franchisee and owner of the cited locations to review and investigate these serious allegations."

-- Brynn Gingras contributed to this report.