Prime Minister John Key should force John Banks to release the statement he made to police when they interviewed him about donations to his 2010 mayoral campaign, Labour says.
The police file on the investigation was released on Thursday but Mr Banks' statement wasn't in it.
Police said they released affidavits on the basis of consent from those who made them.
"If John Key is serious about holding his ministers to any real standards he needs to instruct John Banks to allow his witness statement to be publicly released," Labour's deputy leader Grant Robertson said on Friday.
"Given the damning sworn statements from others in the file, Mr Banks needs to be transparent with the public about what he knew about the so-called anonymous donations."
Mr Robertson says the ACT leader's staff are trying to claim the police made the decision to withhold the statement.
"That is not correct," Mr Robertson said.
"Police clearly stated to us they released the documents of those who authorised them to do so - this is in Mr Banks' hands."
The police file shows Mr Banks solicited a $50,000 donation from internet piracy accused Kim Dotcom and asked for two $25,000 cheques.
He later confirmed to Dotcom that the cheques had been cleared, and then signed an election return listing them as anonymous.
Police decided the return was false but couldn't do anything about it because the time limit for prosecution had passed.