It's a huge grey area, largely up to the NLRB to decide when anti-union campaigners cross the line. They did similar tactics in the Alabama vote and were slapped for that behavior[1], and many other infractions, with an order to re-do the vote[2]. Amazon's execs and lawyers clearly think they have enough to lose (and their workers to gain) that it's worth finding exactly where the line is.
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[1] "The [NLRB] hearing officer also found objectionable Amazon's distribution of "vote no" pins and other anti-organizing paraphernalia to employees in the presence of managers and supervisors. ... U.S. labor law forbids companies from spying on organizing activities or leaving employees with the impression they are under surveillance. It also prohibits other actions if they are found to be coercive." https://www.reuters.com/business/amazon-interfered-with-unio...
go look up what other illegal union busting behaviors they've gotten away with. and look at democrat or republican behaviors, such as biden actively strike-busting the other day
strike busting public unions is good. we should never recognize public unions. there is no middleman to reduce profits with the government, higher wages means we pay more, there's no "evil capitalist" who will get less instead.
An alternative perspective to look at this is that orgs like USPS are services provided to Americans because they're the kind of services that would otherwise be inaccessible to great majority of Americans. For this reason, increasing the wages and potentially attracting better workers and increasing the morale (and thus performance) of existing workers are beneficial for Americans.
The NLRB[1] is supposed to handle it. I have no idea how they would rule on forcing anti-union propaganda on employees today.
And today's SCOTUS seems to want to defang all government agencies' ability to rule on or enforce . . . anything, really, based on their rulings on the EPA and the SEC. Well, unless it's the government trying to enforce on reservation land - that is newly allowed.
They've hired a bunch of outside agencies to help union-busting. My guess is that it came from one of them, and that Amazon will sue them for whatever damages are caused by this.
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[1] "The [NLRB] hearing officer also found objectionable Amazon's distribution of "vote no" pins and other anti-organizing paraphernalia to employees in the presence of managers and supervisors. ... U.S. labor law forbids companies from spying on organizing activities or leaving employees with the impression they are under surveillance. It also prohibits other actions if they are found to be coercive." https://www.reuters.com/business/amazon-interfered-with-unio...
[2] https://www.npr.org/2021/11/29/1022384731/amazon-warehouse-w...