The union representing Manitoba's child welfare workers says it has warned the provincial government for years the system is in crisis.

The Manitoba Government and General Employees' Union has released three letters it sent to the province in 2002 and 2005, raising concerns about the state of the Child and Family Services (CFS) system.

The public inquiry into the 2005 death of Phoenix Sinclair, a five-year-old girl who was killed by her mother and stepfather on the Fisher River First Nation, has cast a spotlight on how CFS workers handled care for the child.

After weeks of CFS workers and supervisors being on the defensive, the union is mounting an offensive attack.

MGEU staff representative Janet Kehler says the letters, posted on the union's website on Friday, warned the province of growing case loads, plummeting staff morale, and concerns over staff training and retention.

But Kehler said some of their pleas have fallen on deaf ears, while major changes that have been made to the CFS system over the past decade have not been handled properly.

MGEU staff representative Janet Kehler says CFS workers are willing to work with the province to improve the child welfare system, but the government is ultimately in control. (CBC)

"The buck stops with them. Their responsibility is with the citizens of Manitoba," she said Friday.

"We, as the union, can write as many letters as we want, and the members can scream and shout, but at the end of the day we're not the decision-makers."

The changes to the system involved private CFS agencies being folded into the government and the creation of 17 new agencies that included First Nations and Métis authorities.

Kehler said those changes continue to impact the system.

She said CFS workers are willing to work with the province to improve the child welfare system, but the government is ultimately in control.

In a statement to CBC News, a spokesperson for Family Services Minister Jennifer Howard said historically, there have been challenges in the child protection system.

The province says in response to numerous reports that were produced after Phoenix Sinclair's death, it immediately added more frontline workers and "established funding formulas that provide funding for one frontline worker for every 25 case files.

"Over the last six years we have more than doubled annual funding to the child protection system. In fact we have never invested more than we are today," the statement read in part.

Howard's spokesperson said since 2006, the province has "more than doubled child welfare funding to about $425 million a year," added more than 280 new positions, boosted training for workers, and added more than 5,000 new foster care and emergency spaces.