The U.S. Supreme Court has made it extremely difficult for taxpayers to challenge IRS regulations by arguably eliminating the distinction between legislative and interpreting regulations. The Court now requires heavy deference to be given to both types of regulations. It is unclear to what extent this type of deference must be given to regulations which have not gone through the full Administrative Procedures Act notice and comment process, and to what extent deference must be given to other forms of IRS guidance, e.g., Revenue Rulings, Revenue Procedures, Notices, etc.