The government is facing tough questions over the downgrading of two tertiary institutions in three months.

The Qualifications Authority downgraded Taranaki's Western Institute of Technology, after losing confidence in its quality of education, and Auckland's Unitec in November over concerns about the way that institution moderated assessments.

WIT's course completion rates dropped from 83 percent to 70 percent between 2012 and 2015.

Tertiary Education Union president Sandra Grey said both institutions have been introducing changes which don't benefit students.

"It's time for both the government and those institutions to listen seriously to the voices of the staff who have been expressing this main concern for quite some time now," Grey said.

Grey said there are fundamental structural issues with how it operates.

"The report says that the staff there really were doing their best under trying circumstances, under heavy workloads."

Several other tertiary institutions have been under investigation by the Serious Fraud Office.