The union representing Manitoba's child-welfare and social workers has lost a court bid to quash a public inquiry into the abuse and death of Phoenix Sinclair, a five-year-old girl, in 2005.

Phoenix Sinclair, seen in an undated photo, was discovered dead in March 2006 on the Fisher River First Nation. A public inquiry into her death is slated to begin May 23. (Family photo)

The Manitoba Government and General Employees' Union (MGEU) had questioned the legal validity and jurisdiction of the upcoming provincial inquiry into the death.

The Sinclair inquiry is set to begin on May 23. It will be overseen by commissioner Ted Hughes.

Ordered by the province in 2006, the inquiry aims to examine how Manitoba's Child and Family Services staff and officials failed to protect the girl, who was killed by her mother and stepfather in June 2005.

The inquiry will also examine how Phoenix's death went unnoticed for months. It wasn't until March 2006 that her body was found wrapped in plastic in an unmarked shallow grave on the Fisher River First Nation.

Lawyers for the union argued last week that deaths of children in foster care are normally examined by provincial court inquests, not public inquiries.

But in a written decision released Thursday, the Manitoba Court of Appeal dismissed the union's motion.