Kiwirail has publicly released the proposal for a new Auckland railway line which the Transport Minister Simon Bridges wanted to be kept secret.
New Zealand First released a series of emails last week showing Mr Bridges' office had urged Kiwirail not to release the business case for the rail line, saying the prospect made it "extremely uncomfortable".
The emails showed Kiwirail had planned to release the document in full, but many parts of the business case released today have now been redacted - including its benefit to cost ratio.
The Third Main rail line would allow for freight and passenger train services to be separated between Wiri and Auckland's Westfield train station.
Read the newly released proposal here:
The report said South Auckland's "current twin track formation has reached maximum operational capacity" and that completing the Third Main Line would remove a significant bottleneck "on this critical section of the national rail network".
Kiwirail's bid to have the Third Main rail line funded in the budget was unsuccessful.
Following the release of the emails between Minister Bridges' office and Kiwirail, Chief Ombudsman Peter Boshier wrote to Prime Minister Bill English seeking an assurance ministers were not flouting the law when dealing with requests for official information.
NZ First leader Winston Peters has now requested the Chief Ombudsman to formally investigate the matter.
Mr Bridges said he was not aware of the business case or what his officials were doing, but he argued they had every right to be contesting the release of the information.
He said parts of the Third Main business case were "materially wrong".