Former Canadian Nuclear Safety Commission boss Linda Keen has stepped down from her role on the CNSC's board of directors, complaining she has been demoted by the government to a position that is an "artificial creation."

Keen was president and CEO of the CNSC when the Chalk River nuclear reactor was shut down last year over safety concerns.

The shutdown led to a worldwide shortage of medical isotopes until Parliament issued an emergency order to restart the Atomic Energy of Canada reactor, overriding Keen's objections.

In a letter addressed to Prime Minister Stephen Harper, Keen said her term as president and CEO had earlier been extended until November 2010, but she was removed from the role on January 15 by an Order-in-Council "without reason or cause."

"I was demoted to a full-time Commission member position of the CNSC. This full-time Commission member position is an artificial creation. Despite my repeated requests, it does not have a job description nor any identified tasks beyond those of a part-time Commission member," she wrote.

In the letter, Keen acknowledges she has launched legal proceedings to have her dismissal overturned, and said it wouldn't be appropriate to continue as a member of the CNSC's board of directors until a court ruling was issued.

Any decisions she made as a board member would be constantly suspected of bias and second-guessed by government officials and applicants before the panel, she said.

"I believe that actually sitting, and making regulatory decisions, as a demoted Commission member when the Government questions my competence and claims to have lost confidence in me, and with my legal case pending against the Attorney General of Canada, would be inappropriate and would place both the CNSC and myself in an untenable position," Keen wrote.

She said the purpose of the letter was to provide notice to the government that she will not be available to sit on any hearing, meeting or panel during its fall hearings.