They can set their own rules, within the bounds allowed by law. It appears to me that they would only be allowed to make this restriction if they prohibit all n

They can set their own rules, within the bounds allowed by law. It appears to me that they would only be allowed to make this restriction if they prohibit all non-work conversation: https://www.nlrb.gov/about-nlrb/rights-we-protect/the-law/employees/your-rights-during-union-organizing https://www.nlrb.gov/about-nlrb/rights-we-protect/the-law/em...