NEW YORK, May 7 (Reuters) - Four current and former partners of Ernst & Young accounting firm [ERNY.UL] were guilty of criminal tax fraud involving questionable tax shelters, a U.S. jury ruled on Thursday.

U.S. prosecutors charged the four in May 2007 on allegations that between 1998 and 2006 they defrauded the Internal Revenue Service by designing, marketing, implementing and defending tax shelters.

Two of the men on trial for the past two months in Manhattan federal court were former partners Robert Coplan and Brian Vaughn. The two others were Martin Nissenbaum and Richard Shapiro, both of whom are on administrative leave from Ernst & Young, a spokesman for the firm said. (Reporting by Grant McCool; Editing Bernard Orr)