The Progressive Conservatives say Bonnie Guagliardo (guh-LARD'-oh) went to the Victoria General Hospital in Winnipeg in February after falling in her home and hitting her head.
The Tories say Guagliardo, who was in her 60s, was given an initial assessment, but went home after waiting six hours to see a doctor.
She died the next morning.
The government says an investigation by the regional health authority is already underway.
But Tory health critic Cameron Friesen says a public inquest is needed to examine what went wrong.
"Manitobans need answers on this, and they need to have a high degree of confidence in the health-care system," Friesen said Thursday.
Friesen suggested the case is similar to that of Brian Sinclair, a 45-year-old double amputee, who died after waiting for 34 hours in an emergency room in 2008.
Friesen released statistics obtained from the Winnipeg Regional Health Authority that indicate a growing number of people are leaving emergency rooms without being seen by a physician.
That happened more than 23,000 times in the 2011-12 fiscal year, an increase of more than 2,000 from the previous year, according to the report obtained under Manitoba's freedom of information law.
Inquests can be called by the government or the chief medical examiner into specific deaths. They are overseen by a provincial court judge and witnesses testify under oath.