Public unions aren't like private unions that negotiate labor terms with a single company or workplace. Public unions have outsize influence because they can often buy the politicians who are supposed to represent taxpayers. The unions effectively sit on both sides of the bargaining table.
Thus over time they have been able to extort excessive wages, benefits and pensions, as well as sweetheart contracts like the monopoly provision of health insurance.(Peoria County pays $2 out of every $3 dollars for employee health benefits and yet employees complain) Their focused special interests trumps the general interest of the taxpayers, who are busy making a living and lack the time to focus on politics other than at election time or amid a financial crisis, often too late, except in the case of Wisconsin Governor Walker's brave move to stop the monopolizing.
Students of democracy from Tocqueville to Mancur Olson have pointed out that the greatest threat to self-government comes from the tendency of democracies to become barnacled with special interest that vote themselves more benefits than society can AFFORD. This is the crisis of the modern entitlement state, which is unfolding from Illinois to California, Greece, Italy and Washington, D.C.. Wisconsin is a critical test of whether democracies can reform before the crisis becomes debilitating.
Much of this information above comes from what many leaders have said and written' leaders who have a great concern over the future of this republic.
Unions had a great effect on how the 12 Democrats on the Peoria County Board voted to influence the vote of these Democrats. Union leaders sat behind board members or in the audience at every meeting concerning the vote for the public to pay 72% of the cost of the total museum. (instead of the 33% promised) One Democrat board member agreed with my reasons to vote no on the project but said he was "under too much pressure to vote no".