Is this just another reason to get rid of public sector unions?

Many corporations volunteer their employees for a community service day/project. The fact that they wish to volunteer in an area that they are professionally involved in makes quite a lot of sense. To everyone but the greedy unions who jealously guard every inch of their turf. In their minds if the parks aren't clean enough they need to hire more workers to pay union dues! No one mentions that if the union workers actually did their jobs there would be no need for volunteers to help.