Not all workers have joined the union and wouldn't get paid by the union to strike. But unions use sympathy strikes against companies that might retaliate against their workers if they strike, Tesla has already made threats. So going by how many of the workers at Tesla are striking or not is not a good measurement.
The union is offering free memberships and 130% of normal pay. Tesla employees still don’t want to strike [1]. This is why the unions are using these extreme tactics.
