Communism is an ideology that seeks to establish a classless, stateless social organization based on common ownership of the means of production. It is usually considered a branch of the broader socialist movement that draws on the various political and intellectual movements that trace their origins back to the work of Karl Marx.
Communism was abhorent to the Race on many levels. The Soviet Union, a not-empire that embraced communism, had been founded on the regicide of its former emperor, a notion that horrified the monarchist Lizards. In China, a country that did not easily accept Race rule, the most organized and effective resistence was offered by the Chinese Communist Party.
The Race wasn't the only one wary of the spread of Communism. A driving component of NaziGermany's ideology was an anti-communism. And while the United States supported communist resistance in China, it did so somewhat grudgingly. The US had long had an anti-communist bent to its politics.
In fact, the brutal totalitarianism of the Soviet political system both before and after the war against the Race made communism repugnant to anti-totalitarians of every stripe.