The Department of Immigration and Citizenship has come under fire for taking too long to respond to and process invalid visa applications.
The department takes anywhere between one day and two years to assess an application as invalid or incomplete, a new report by the Immigration Ombudsman has found.
Professor John McMillan said many applications were ruled invalid due to issues such as missing paperwork.
He was concerned the delays put some applicants at risk of being declared unlawful or having their visa options severely limited.
The Invalid Visa Applications report identified more than 200 cases between 2006 and 2008 where this had occurred.
"Processing delays and inconsistencies could have serious consequences for the immigration status of applicants," Prof McMillan said.
The report found the average length of time to process an application as invalid was 38 days.
Prof McMillan recommended applications be assessed in a more "timely manner".