This can be written books about
Workers unions are for making the power more equal between workers and companies. If the CENTRAL union is strong, then can workers in DIFFERENT companies cooperate to put pressure at to bad behaving companies by strikes, or by refusing to make transports to them. BUT in some countries have worker union leaders being STUPID and put up UNREALISTIC DEMANDS, which companies can't fullfil and still being profitable, so IF the worker union demand to much, then the companies will quit or go bankruptcy and then will the workers be out of work, which would be BAD for the workers too, because they would be out of work
So best is to have a BALLANCE between the workers and the companies so BOTH find the situation ok/good.
(In my home contry the woker unions are strong. Earlier they had to high demands sometimes, but now it's good ballance so there are almost never any strikes or biger disagreements.)
Do you mean how to DEVELOP a LOCAL workers union where you work?
Such is very hard when the union is weak IF the company is bad =Where an union are most needed. Because then it's big risk for complainers to lose their employment. DOLE have SOME protection, but I don't know how weak. Perhaps it's strong in SOME cases, but it can't be strong in general, because otherwice couldn't some very bad companies act as they do in the Philippines...
(E g GOOD workers are replaced after 6 months, because the company can avoid to pay some fees then. That's a very UNFAIR LAW, which some bad companies use much