>Management is legally required to make concession

This is false. The NLRB explicitly says so:

> It is an unfair labor practice for either party to refuse to bargain collectively with the other, but parties are not compelled to reach agreement or make concessions.[0]

They are only required to bargain 'in good faith.' Withholding benefits they would normally give is an intimidation tactic and an attempt to maintain leverage.

[0]https://www.nlrb.gov/about-nlrb/rights-we-protect/your-right...