Action on Spell sunder

[Firewarrior44]

Is the barbarian's Spell Sunder (Su) a Standard action or an attack action?

It does not specify that is is a lesser action explicitly and thus would default to a standard.

However it also uses sunder checks / and references the sunder combat maneuver which can be used in place of attacks.

[GM Rednal]

Quote:

Once per rage, the barbarian can attempt to sunder an ongoing spell effect by succeeding at a combat maneuver check

It seems pretty clear to me that this is done as a combat maneuver (specifically, a Sunder maneuver), and can be done any time you can do that and have a valid target.