In a First Office Action ruling, news sources and the FOSS Patents blog are reporting, the U.S. Patent and Trade Office shot down all 21 claims made by Apple's (AAPL -0.35%) in one of its key patents, U.S. Patent No. 7,844,915. This is considered an essential patent for Apple if it is to keep the pinch-to-zoom feature to itself.

A First Office Action is only a tentative ruling, but it does give more ammunition to Apple's main rival Samsung in its attempt to persuade a Judge to overturn a previous patent infringement ruling against it.

Last August, a California jury ruled in Apple's favor, saying Samsung had infringed on six out of seven of Apple's patents. The court ordered Samsung to pay Apple $1.05 billion, and posed the threat of a permanent ban on certain Samsung products being sold in the U.S.

However, this is the third USPTO tentative ruling to go against Apple's patent claims since that trial. In October, all 20 claims of U.S. Patent No, 7,469,381, the so-called "rubber-banding" patent, were held to be invalid.And earlier this month, each of the 20 claims made in U.S. Patent No. 7,479,949, also known as the "Steve Jobs" patent, were discounted.