I don't personally believe that not requiring union membership makes it any harder to unionize. It's an issue of freedom of choice. If we were banning lower governments from banning/severely undercutting unions, I would support this. But in the current form of the bill it doesn't seem like it does anything that really helps workers.
You are mistaken. Unions need money to organize and operate. Allowing workers to receive the benefits of union membership without paying the dues invariably harms unions and unionization efforts.
As stated earlier, "So when the POWER Act passed, unions were no longer forced to represent non-union workers ... therefore there was no longer a free-riding problem legally justifying agency fees"