[datavirtue]

If they aren't allowed to strike why do people keep signing contracts with them?

[malcolmgreaves]

Because the police union covers for cops that break the law.

[93po]

there's lots of other benefits (for cops) for joining, also the general vibe with police work in the US is that if you're not on board, you're going to get harassed and threatened (and rarely assaulted/murdered) until you leave (see: thin blue line)