Obviously and overwhelmingly left leaning. You can't be pro-business and pro-unions, and these values are core to the right and the left respectively. I feel like I'm stating the most obvious facts here.
Interesting. I see both sides representing the interests of the corporations that fund their campaigns. Both advertise that they are for the working class. Neither actually is.
If by "both sides" you mean american democrats and republicans, sure. Although republicans are much worse for the working class than the democrats. Both are at the heels of capital, one side is just that much more overt and aggressive about it.
In the rest of the world though, there are actual leftist movements who are genuinely standing for the working class. But they don't get much power these days, and things are mostly going backwards for worker's rights globally.
One thing is sure though, it's that any progress workers enjoyed in the past didn't come from the right. Paid leave, minimum wage, healthcare, retirement... it all came from the left.
Not sure about the rest of the world, civil rights and OSHA are counter examples to the "all came from the left" claim in the US. Anyway, better not reply, political discussion isn't allowed here.
I can only recommend a quick read through the Wikipedia page for Syndicalism: https://en.wikipedia.org/wiki/Syndicalism