I am currently studying labour unions, and I need to know some advantages and disadvantages of unions in general

A very simple resource is your local AFL-CIO, if you have one.

One advantage of labor unions is that they allowed the workers to organize so that they would have better representation when it came to negotiations with the employers. From an employee's standpoint, the benefits of union representation include:

• better wages • protected rehire rights • better benefits • full or majority airfare to job site • notification of job openings • protection from unsafe or illegal working conditions
• professional representation in labor or management disputes • protection from discrimination and arbitrary termination • camaraderie

A disadvantage to unions? When the union calls for a strike, the worker strikes. The worker does not cross the picket line, the worker honors the strike. This may mean going without wages until the strike is settled. Another disadvantage could be the union fees. But the benefits of belonging to the union would offset that. One more disadvantage may be the politics of the union. The worker may not agree with who the union backs as a candidate for public office, the worker may not back a policy. Just like any other job!