It was Monday, after school. Toni Coral and four of her fellow high school teachers in Hamtramck, Mich., were finalizing plans for the next morning.

They would meet at 5:30 for the two-hour drive to the statehouse in Lansing, Mich. Republicans were expected to pass legislation on Tuesday that would cripple, if not eliminate, unions. Coral and the other teachers were taking the day off, as allowed by their contract, to join thousands of fellow union workers in protest.

“Bring a towel,” the more experienced teacher said to Coral and her colleagues. “Bring a bottle of water, too.”