If I call for a meeting I am requesting that a meeting be held. I am probably not in a position of power but it's my belief that we need a meeting. If I call a meeting I have some authority to require others to be present at my meeting, often because I am the boss.

By the way, I should probably say that these kinds of subtle differences might vary from country to country. I am from the UK. The meaning might be slightly different in the US and other english-speaking countries

Great answer! Couldn't agree more to 18ck's answer. Syed