The strikers. And since most of the working class lives paycheck to paycheck, a war chest is necessary to pay the bills during the strike. That’s largely what union dues are for.

For most people, a strike that lasts long enough to force concessions will lead to losing their job entirely, and likely being evicted as well if they don’t have another source of income. You could gamble on there being too many evictions to enforce, but it is a gamble and many people will certainly be affected regardless.

Strikes are a great tool, but the short term cost is mostly borne by the strikers. Effective implementation requires resources and organization.