OTTAWA — Elections Canada is asking a judge to unseal up to a staggering five million pages of Conservative party documents tied to allegations the party broke federal election laws with a controversial advertising campaign in the 2006 election.

The demand is the first major development in the case since investigators raided Conservative party headquarters last year.

Elections Commissioner William Corbett and lawyers with the federal public prosecution service have asked the Ontario Superior Court of Justice to review the documents after the party claimed they contained confidential information that is protected by solicitor-client privilege.

The legal roadblock has "stymied" the investigation and prevented authorities from determining "whether the evidence points to additional investigative activities or provides a sufficient basis for the recommending or not recommending of charges," Elections Canada told the court.

"The investigation cannot adequately proceed because the number of documents over which privilege is claimed, and which investigators and our forensic accountants are therefore unable to review, results in potential evidence not being available to investigators," Ronald Lamothe said in an affidavit supporting the application.

A Conservative spokesman said the party would have no comment on the case until their arguments are made in court.

RCMP computer experts cast doubt in the affidavit on Conservative claims that it would be too onerous to review the millions of computer documents to weed out records that might be available to Elections Canada without violating privilege.

The Conservatives have already waived the solicitor-client privilege they originally claimed on 13 of 16 boxes of paper documents that were sealed after an Elections Canada raid on party headquarters last April.

The search followed a year-long inquiry into $1.3-million worth of Conservative advertising the electoral agency says may have broken federal election law.

The Conservatives have said they broke no laws and are fighting Elections Canada in a separate court action.

In an affidavit used to obtain the search warrant, an Elections Canada investigator claimed the party used a complicated cash-transfer scheme to skirt its national campaign spending limit by more than $1 million.

In a series of transactions that were controlled by party headquarters during the campaign, the Tories transferred thousands of dollars to more than 60 riding campaigns. Those local campaigns then flipped the money back to the party as payment for national radio and television ads that were broadcast in their regions.

Lawyers for the Conservative party succeeded in clamping a legal seal on the documents Elections Canada are seeking. The printed pages and millions of electronic pages stored in computers are being held by Elections Canada as well as the RCMP Integrated Technological Crime Unit in Ottawa.

Lawyers for the agency and the prosecution service cited dozens of cases in the application for a judicial review. They asked the court to determine whether the documents are protected by solicitor-client privilege and order them returned to the elections commissioner if they are not.

It follows a hearing in Federal Court earlier this week where the two sides are waging a separate legal battle over the party's claim that Chief Electoral Marc Mayrand should have recognized the ad spending as legitimate expenses for the local candidates.

The party's former general counsel, Paul Lepsoe, stepped aside from that case after the party claimed solicitor-client privilege for the documents seized in the raid. Lepsoe was counsel for the Conservatives when they designed the ad strategy.