Ill. Admin. Code tit. 14 § 470.290
Where a direct price comparison is not utilized as provided elsewhere in this Part, it is an unfair or deceptive act for a seller to use such terminology as "sale", "sale prices" "Now only $____" or other words and phrases that imply a price savings unless the price of the product is reduced by a reasonable amount from the product's former (regular) price as determined in accordance with Section 470.220 of this Part. If the seller reduces the price by 5% or more a rebuttable presumption shall exist that the price reduction was of a reasonable amount. However, the term "sale" can be used in an advertisement where not all items are offered at a reduction to regular price if such items are clearly identified.
Ill. Admin. Code tit. 14, § 470.290