The three men have been called in to be "heard as manslaughter suspects" following the disco fire late Friday, the public prosecutor's office said.
Witnesses said fireworks unleashed a blaze at the Colectiv nightclub in a former shoe factory which was followed by a stampede as terrified clubbers scrambled to get out.
Authorities said three more badly burned victims succumbed to their injuries yesterday, bringing the death toll to 30.
Romanian media and witnesses have questioned safety regulations at the club. Witnesses spoke of the absence of an emergency exit.
The disco did not have the required authorisation to hold concerts or to stage pyrotechnic displays, the secretary of state at the interior ministry, Raed Arafat, has said.
Prosecutors must now look into who should have ensured such authorisation was granted.