The Internal Revenue Service has updated its guidance concerning travel in two important ways. First, there are new rates for substantiating business travel expenses with per diem allowances, rather than with actual expenditures. Second, there are new SIFL (standard industry fare level) rates for determining an employee's income from using an employer's aircraft for non business travel. 

IRS Circular 230 Notice
Internal Revenue Service regulations state that only a formal opinion that meets specific requirements can be used to avoid tax penalties. Any tax advice in this communication is not intended or written to be used, and cannot be used by a taxpayer, for the purpose of avoiding penalties that may be imposed on the taxpayer, because it does not meet the requirements of a formal opinion.