29 CFR 825.401: Filing a complaint with the Federal Government.

(a) A complaint may be filed in person, by mail or by telephone, with the Wage and Hour Division, U.S. Department of Labor. A complaint may be filed at any local office of the Wage and Hour Division; the address and telephone number of local offices may be found in telephone directories or on the Department's Web site.

(b) A complaint filed with the Secretary of Labor should be filed within a reasonable time of when the employee discovers that his or her FMLA rights have been violated. In no event may a complaint be filed more than two years after the action which is alleged to be a violation of FMLA occurred, or three years in the case of a willful violation.

(c) No particular form of complaint is required, except that a complaint must be reduced to writing and should include a full statement of the acts and/or omissions, with pertinent dates, which are believed to constitute the violation.