How do the Weedpatch camp migrants prepare for the rumored invasion of the Saturday night dance in The Grapes of Wrath?

The Joads wind up at Weedpatch camp, a government-sponsored facility where the migrants govern themselves. This spares them from having to worry about corrupt police officers, which are normally a major problem for migrant workers in this part of California. The local Farmers' Association, however, are none too happy about the camp. They see the place as infested with Communist trouble-makers who will agitate for higher wages than the twenty-five cents an hour that local ranch owners currently pay their workers.
The boss of the local ranch Mr. Thomas tells Tom Joad and Timothy and Willkie Wallace that the Farmers' Association are planning to send some hired instigators into Weedpatch during the Saturday night dance to stir up trouble and cause a riot. Then the police would have an excuse to raid the camp and close it down for good.
The chairman of the camp committee, Ezra Huston, prepares for the trouble-makers' imminent arrival by hiring twenty men to look out for them in the hope of avoiding a riot. Nevertheless, a handful of instigators manage to find their way into the camp and try to start trouble. Thankfully, they're apprehended in time and evicted from the camp, but not before Ezra Huston gives them a dressing down for turning against their own people.