Several dozen Walmart workers in Southern California staged a one-day strike on Thursday, according to workers and union officials, a move that culminated in a rally of some 250 workers and supporters in front of a Walmart store in Pico Rivera.

The strikers, who union officials said came from nine Walmarts in the Los Angeles area, said they were mainly protesting what they said was management’s frequent retaliation against employees who spoke up about working conditions.

Several of the workers, who said this was the first-ever strike against Walmart in the United States, also said they were protesting low wages and short hours.

Manuela Rosales, 25, who works in the cellphone department of the Pico Rivera store, said she walked out on Thursday, missing her afternoon shift, because “when we speak out, they cut my hours in retaliation and they have me pull pallets, which is very hard work.” She added, “I’m a single mom and I can’t afford them cutting my hours.”