The U.S. Postal Service processing and distribution center in Tucson has been cited by safety regulators for a “willful safety violation” involving the improper operation of a powered industrial truck.

The Postal Service faces a proposed penalty of $70,000, the U.S. Department of Labor’s Occupational Safety and Health Administration said.

OSHA’s investigation of the facility, located at 1501 S. Cherrybell Stravenue, was prompted by a complaint that an untrained, uncertified supervisor had operated a powered industrial truck during an evening shift.

The truck, which is used to move large quantities of mail, requires training and certification to operate. When two of three certified truck operators did not report for their shift, a supervisor without training or certification operated the truck, exposing workers to potential injuries, OSHA said in a news release.

A willful violation is “one committed with intentional knowing or voluntary disregard for the law’s requirements, or with plain indifference to worker safety and health,” OSHA said.

Violations of OSHA’s powered industrial truck standard are among the top five types of violations most commonly cited by OSHA in fiscal year 2012.

The U.S. Postal Service has 15 business days from receipt of its citation and penalty to comply, request an informal conference with OSHA’s area director or contest the findings before the independent Occupational Safety and Health Review Commission.