Found on www.irs.gov
Bulletin: 2012-26
June 25, 2012
Notice 2012-40

All employers that are treated as a single employer under 414b,c,or m, relating to controlled groups and affiliated service groups, are treated as a single employer for purposes of the $2,500 limit.  If an employee participates in multiple cafeteria plans offering health FSA's maintained by members of a controlled group or affiliated service group, the employee's total health FSA salary reduction contributions under all of the cafeteria plans are limited to $2,500. However, an employee employed by two or more employers that are not members of the same controlled group may elect up to $2,500 under each employer's health FSA.