How did living in company towns make union membership more difficult for workers?

B.) Company guards and agents spied on and reported workers.

Explanation:

People who worked for company and lived in company towns itself faced many disadvantages and problems. They were often spied and watched continuously by their officials or other people. They could not enjoy their personal life as well. Even if they step out of their houses and move into the streets they are viewed by someone. They cannot enjoy or lead a comfortable life as such. Even if they want to spend their time with their family they could not do even that also. It is a place where they are indirectly treated as prisoners.

I believe the answer is: Because company stores didn't sell goods to workers who were in a union

And the working sites usually located far away from the metropolitan area (such as on top of the mountain or in the middle of the desert). This provide the workers with no other choice but to leave the union if they want to be a part of the work forces and live in company towns.