At a time when retailers are slashing prices to attract last-minute Christmas shoppers, many stores aren't marking down certain popular gift items at all.

That's because of little-known manufacturer agreements that require retailers to refrain from discounting, especially in any advertising. If retailers don't comply, manufacturers sometimes stop subsidizing ads or cut off supplies altogether.

This season's products affected by pricing agreements include Guitar Hero World Tour Band Kit from Activision Blizzard Inc., documents show. The video musical game has been priced at $189 at Best Buy Inc., Circuit City Corp. and Toys "R" Us Inc. since its October release. A new rival product, Electronic Arts Inc.'s Rock Band 2 Special Edition, also has been retailing for that price at all three outlets.

"Activision Publishing Inc. would like to inform you of its Minimum Advertised ('MAP') program," the game maker wrote to retailers in a letter dated Sept. 24. The letter, which says it won't subsidize any advertisements that violate the policy, goes on to list 19 products and their minimum prices, including Guitar Hero and the James Bond: Quantum of Solace videogame.

Activision Blizzard didn't respond to requests for comment.