I would say it takes a standard action.
From "Actions in combat",
A standard action allows you to do something, most commonly make an attack or cast a spell.
Consider this: you are turning your attention to a creature and forcing it to approach. This should require some amount of effort. Since it is a spell effect, it's safe to assume it would require a comparable amount of effort as would concentrating on an active spell take, and concentrating on a spell is a standard action.
Approaching from another perspecitve, any unusual type of action is normally spelled out in description ("as a free action, you can..."). If it doesn't and you need to "do something", it would default to a standard action instead.