Opposition parties are hoping to get to the bottom of a row between Natural Resources Minister Gary Lunn and the head of the nuclear safety watchdog on Wednesday when the two are expected to appear before a House committee.

On Tuesday, MPs on the natural resources committee voted to summon both sides to speak about the fallout over the closure of the nuclear reactor in Chalk River, Ont., which produces much of the world's medical isotopes.

Lunn and Canadian Nuclear Safety Commission president Linda Keen have exchanged barbed letters since the facility was shut down and then forced to reopen as the shortage of isotopes became critical.

In a letter leaked to the media, Lunn asked Keen why she shouldn't be fired for recommending the closure of the reactor, operated by Crown corporation Atomic Energy of Canada Ltd. 

Keen responded with a letter accusing the minister of interfering with the independence of the arm's-length watchdog.

"It's unprecedented and very surprising and that's why we called for this meeting," Liberal critic Omar Alghabra said.

The 50-year-old reactor produces two-thirds of the world's supply of isotopes used for medical procedures.

The facility was ordered shut last November after failing to meet safety standards concerning cooling pumps not hooked up to back-up power supplies.

On Dec. 10, a ministerial directive ordered the watchdog to reopen the site. The agency refused, saying the system needed to be installed to prevent meltdown in disasters such as earthquakes.

A day later, the House of Commons overturned the watchdog's decision by passing an emergency measure, ordering the reactor to restart on Dec. 16 for a 120-day run.

At a CNSC meeting earlier in the month, it was revealed that two earthquakes occurred in the Chalk River area since the facility's reopening, though the AECL said neither was strong enough to be a safety concern.