The federal government has threatened to fire the head of Canada's nuclear watchdog over the Chalk River reactor shutdown, and she responded Tuesday by vowing to fight back through the courts.

Natural Resources Minister Gary Lunn wrote a letter to Canadian Nuclear Safety Commission (CNSC) president Linda Keen on Dec. 27 in which he questions her judgment and informs her he is considering having her removed from the post.

The letter, which was leaked to the Ottawa Citizen newspaper, was written in the wake of last fall's shutdown of the Chalk River nuclear reactor and the global shortage of radioisotopes that resulted from it.

Keen responded on Tuesday with an eight-page letter accusing Lunn of improper interference and threatening to fight in court any attempt to remove her from her job.

Keen's letter, which has been posted on the CNSC website along with Lunn's, also suggested his letter would have a negative impact on other quasi-judicial
agencies that are supposed to be at arm's-length from government.

"I would therefore ask you to carefully consider the significant chilling effect your recent actions could have on the practices and decisions of other tribunals who are responsible for important work on behalf of Canadians," Keen wrote.

Additionally, Keen said she has asked the privacy commissioner and the RCMP to investigate how Lunn's letter was leaked to the media.

The 50-year-old Chalk River reactor, which generates two-thirds of the radioisotopes used around the world in medical procedures, closed down on Nov. 18 due to safety concerns.

A ministerial directive on Dec. 10 ordered the CNSC to reopen the site. The agency refused, insisting a backup safety system be installed to prevent the risk of a meltdown during an earthquake or other disaster.

On Dec. 11, an emergency measure passed through the House of Commons overturning the watchdog's decision and the reactor was restarted for a 120-day run on Dec. 16.

Lunn wrote that Keen's response to the situation "cast doubt" on whether she possessed the "fundamental good judgment required by the incumbent of the office of president of the commission.

"These doubts have led me to question whether you should continue to serve as president of the commission."

Lunn said he was considering a recommendation to cabinet to have her removed as president of the commission, but to allow her to continue to serve on the commission.

He wrote that the watchdog may not have "appropriately considered" the effect of the shutdown on the health of Canadians.

He gave Keen until Thursday of this week to respond.

Keen became head of the commission in 2001 and is currently serving her second five-year term.

Lunn's office has not commented.

With files from the Canadian Press