Criminal investigation for sheep exporter

Australia's biggest sheep exporter is under criminal investigation over conditions on board its Middle East-bound vessels.

Perth-based Emanuel Exports has been ordered by the Department of Agriculture to "show cause" why it should hold an export licence.

The department on Friday also said a criminal investigation has been launched in response to footage released by Animals Australia showing sheep in horrific conditions on board ships to the Middle East during the northern hemisphere summer in 2016.

A department spokeswoman said it included allegations of overstocking, failing to have sufficient food and water available, animal injury and illness not being treated, and accredited vets and stockmen leaving vessels prior to unloading.

A number of witnesses are being questioned.

Western Australia's Agriculture Minister Alannah MacTiernan said the investigation was "a long overdue exercise of responsibility" by the federal government.

"They have for so long allowed bad conduct in the industry to go unpunished," she told AAP.

Ms MacTiernan also called on the Turnbull government to release export licence documents to help the state Labor government's pursuit of legal action against Emanuel Exports.

She's argued it was unacceptable the government had been hiding behind commercial confidentiality.

Emanuel Exports deferred comment to the Australian Livestock Export Council.

A spokesman told AAP it wasn't appropriate to comment while the investigation is underway, other than to say the company had always been fully-cooperative and compliant with requests and actions from the regulator.

Lawyers for the company have reportedly returned a lengthy submission to the "show cause" notice.