Heidi's Law This bill revises the Mandatory Guidelines for Federal Workplace Drug Testing Programs to include testing for methadone and newly identified drug substances. The Department of Health and Human Services must revise the guidelines to (1) expand the opiate category on the list of substances authorized for testing to include methadone, and (2) add any new drugs which may not have been previously included on such list. The Department of Transportation must update its regulations containing procedures for transportation employee workplace drug and alcohol testing programs to include testing for methadone and newly identified drug substances.