With five locations, in Northeast Philadelphia, Ridley Township, Bensalem, Clementon and Turnersville, Nifty Fifty's restaurants are nostalgia-themed throwbacks to the glory days of sock hops and drugstore-fountain milkshakes. "Not just another restaurant," the company touts on its website, "but a way of life."

Federal prosecutors, in a criminal case filed Wednesday, say that way of life included a long-running scheme by the company's owners and top managers to evade more than $2.2 million in federal employment and personal income taxes by skimming mountains of cash from the 26-year-old chain. Participants in the alleged conspiracy improperly recorded $15.6 million in gross receipts, according to charges filed by U.S. Attorney Zane David Memeger.

Charged with cheating the IRS, evading payroll taxes, bank fraud, and related offenses were: Robert Mattei, 73, of Delray Beach, Fla.; Leo McGlynn, 52, of Swarthmore; Brian Welsh, 48, and Joseph Donnelly, 49, both of Springfield, Delaware County; and Elena Ruiz, 46, of Drexel Hill.

"We deeply regret our misconduct and accept full and complete responsibility for our actions," the company said on behalf of the defendants. "We have been fully cooperative with the IRS to resolve these issues and have repaid all back taxes and penalties. We will continue to run each of our five restaurants in full compliance with the law. We wish to thank all of our employees, friends and business partners for their continued support as we move forward. Because this matter is still in the court system, we can have no further comment on this matter at this time."

The eight-count "criminal information" — a formal complaint, which is short of a criminal indictment, and often indicates that a plea deal is in the works — alleges that employees of the restaurants received only a portion of their compensation in official paychecks and the rest in skimmed cash, which allowed the defendants to rig the books. A similar cash payment scheme was allegedly used with some of the company's suppliers, the information alleges.

"Between January 2006 and August 2010 alone," according to the charges, "the defendants concealed approximately $4.1 million in skimmed cash in safe deposit boxes for the exclusive benefit" of Mattei and McGlynn, who are 50-50 co-owners of the company, according to the charges. Other defendants also are alleged to have stashed cash in personal safes.

It is further alleged that Mattei, McGlynn, Donnelly, and Welsh committed bank fraud by submitting to the bank bogus tax returns in order to secure several business loans.

Ruiz, Mattei's daughter and office manager for the company, is charged with receiving skimmed cash and filing false tax returns that inflated expenses and deductions.

If convicted, the defendants face fines and possible prison sentences.

Contact Michael Matza at 215-854-2541 or mmatza@phillynews.com.