I don’t think it’s because of mandates. It’s a tight labor market and quits and strikes are more likely to happen when labor is hard to come by. Have any of the John Deere union leaders cited vaccines? Kellogg’s? No, they cite poor working conditions and low wages at a time of record profits.
https://mattbruenig.com/2021/10/31/is-the-strike-and-quit-wave-due-to-vaccine-mandates/