I admit to not looking it up, but as you stated, yes that is the normal union practice and kind of most of the point of paying dues. To pay for the administration needed for an organization (lawyers, media PR people, records keepers and all that stuff) but also a massive portion is meant as a “not only can we withhold our labor collectively and shut your profit-making down completely, but we can pay the workers to NOT work for [whatever amount of time].” Withholding labor indefinitely obviously forced management and owners to either decide that they legitimately cannot give in to worker demands (which is never the case. They always choose to not do so, but they obviously CAN) and pack it up ie shut some location down or give in and hammer out a deal and contract to end the strike. There’s also the fun third options of trying to hire a fuckload of scabs or, the best option, having the government come in and and shot a few strikers and the rest get the message. Obviously I’m being sarcastic calling those “good” just in case anyone misreads that.

So, I to assume this is a mixture of workers’ private savings and such + union funds and the owners have identified a general timeline for when the money will simply be gone.