Australian Federal Police officers raided the AWU headquarters in Melbourne and Sydney in October 2017 as part of an investigation by the Registered Organisations Commission.

The ROC was investigating donations the AWU made to activist group GetUp! when Labor leader Bill Shorten was in charge of the union.

But the raids drew scrutiny because journalists arrived at the offices before police, thanks to a tip-off from the office of federal Jobs Minister Michaelia Cash.

Senator Cash's media adviser David de Garis later quit over the incident.

The AWU took Federal Court action soon after the raids, believing they were unlawful.

A hearing was scheduled for August 1, with Senator Cash subpoenaed to give evidence.

But on Wednesday the union sought to delay the hearing, saying issues had arisen from the length of the AFP investigation.

Police previously claimed public interest immunity on the basis that the release of documents would prejudice its investigation.

AWU's legal counsel Herman Borenstein QC said the federal police investigation was due to be finished at the time that the raids court hearing was due to start.

Justice Mordecai Bromberg agreed to move the case, vacating the August date and locking in a five-day hearing starting on September 3.

Senator Cash was subpoenaed in May to give evidence at the hearing, along with Mr de Garis, Fair Work Ombudsman employee Mark Lee and ROC official Chris Enright.

New subpoenas will be issued to change the date when witnesses will be called, the court was told.

Australian Associated Press