NKVD Order No. 00485, called

"On the liquidation of the Polish diversionist and espionage groups and POW units,"

was approved on August 9, 1937 by the Party's Central Committee Politburo, and was signed by Nikolai Yezhov on August 11, 1937.

It was distributed to the local subdivisions of the NKVD simultaneously with Yezhov's thirty-page "secret letter," explaining what the "Polish operation" was all about. The letter was entitled,

"On fascist-resurrectionist, spying, diversional, defeationist, and terrorist activity of Polish intelligence in the USSR".

 Stalin demanded the NKVD to "keep on digging out and cleaning out this Polish filth." 

The operation was the second in a series of national operations of the NKVD, carried out by the Soviet Union against ethnic groups, including Latvian, Finnish, German, Romanian an others, based on a theory about the "fifth column" residing along its western borders. The Russian Communist Party classified these peoples as a "hostile capitalist surrounding."