I'm more familiar with pre-20th century stuff and tend more towards musicals and opera than straight plays, but I'm a big fan of the great 18th century Bourgois revolutionary operas William Tell (Rossini) and La Muette di Portici (Auber). The first was the trigger for the 3 days in July, the latter for the Belgian Revolution.

There's also the ballad musical Reedy River, about the aftermath of the Australian 1891 Miner's strike that triggered the formation of the Australian Labour Party, the first Social Democratic Party to take power in the world.

If your looking for Socialist Operas/Plays/Ballets, the Maoist era plays (often filmed before staged, but they're all quite stagey in scripting) are better than their reputation suggests. The Red Detachment of Women is a particular favourite, though I prefer the ballet to the other adaptations.

For 20th-century straight plays, I recommend John Crawford, particularly his "Rocket Range" which examines the effect of the Woomera Rocket Range opening on local Aboriginal Communities.