If you have to get a license from the state to make a living at a certain trade, that’s called occupational licensing. You will not find any mention of it in either the American or the Iowa Constitutions, but the custom extends far back in history, medieval guilds being the example most familiar to us.
Unfortunately there has been an explosion of occupational licensing laws, beginning in the late 20th century, and Iowa is one of the the worst offenders. You can see a list of all 111 occupations in Iowa requiring a license here.
The pure libertarian position – there should be no occupational licensing laws – makes sense on a theoretical level, but we are where we are.
I believe a recent Nebraska law, promoted by a Libertarian in their legislature, might make more sense. Every 10 years every occupational licensing law has to be re-examined and re-authorized. Without compelling evidence, based on hard data, that the licensing requirement significantly increases public safety, it is eliminated.
An alternative is simply to give anyone who is licensed to work in one of the other 49 states a license to work in Iowa. This eliminates entire Iowa bureaucracies and saves Iowa taxpayers money, not to mention removes a barrier to moving to Iowa, a state that should be encouraging people to move here, not discouraging them from doing so.
Toward that end I suggest a new state slogan.
“Iowa, the state that works.”