The pigs, No mystery as to whom they represent, They even steal our protagonists' eggs and they're determined to put an end to this robbery once and for all.
The pigs are usually encamped in elaborate building structures which represents the deeply embedded and far reaching capitalist system while our heroes, the birds, can only ensure an end to the robbery by destroying them. Parallel to the proletarians' task to smash the state machinery. If otherwise the game would be a defensive one (reform, fending off against the porks)
To top it all off, birds can fly, Which symbolizes the infinite potential and rise of living standards of the proles once their shackles to the exploitative system is gotten rid off.
Very clear that the main character being red is an homage to the Soviet Union.