That's just in the US though. There's a whole world out there that is not the United States.

The British Medical Association certainly claims to be a trade union.

https://www.bma.org.uk/about-us/bma-as-a-trade-union

And they have engaged in collective action - e.g. the junior doctors strike.

https://www.theguardian.com/society/2016/sep/01/what-you-nee...