The government was unaware when it formed the new panel in April 2013 that it was inheriting a backlog of 7,000 old-age security and Canada Pension Plan disability appeals from the former pension review tribunal, Kenney told a parliamentary committee.
He said he was "dismayed to learn that there was a backlog of several thousand cases" when he took over the portfolio from Diane Finley in July 2013. The backlog has now swelled to more than 11,000.
Kenney said the former tribunal did not share the backlog information with the Conservative government when it formed the new body, which was ostensibly created to provide a more efficient appeal process for those denied employment insurance, CPP and old-age security benefits.
It was also supposed to save Canadian taxpayers $25 million a year by streamlining the appeals process, even as stakeholders warned that the plan to replace nearly 1,000 part-time referees with 74 full-timers could result in a 16-month backlog.
"This was an unexpected legacy backlog, and ever since I was appointed I have been working very intensively with the chairwoman of the tribunal on fixing it," Kenney said.
But Liberal MP Rodger Cuzner pointed out that Murielle Brazeau, the head of the tribunal, recently told the same committee that she knew of the backlog from Day 1 and discussed it with the minister's office "throughout the whole process."
"Six months in, you saw the problem, you identified the problem," Cuzner told Kenney.
"Six months in, you increased it by 10 or 11 staff when there were even part-time positions that could have been filled. And there were disabled Canadians — some had been waiting for two years at that point to have their appeals heard."
He added: "You inherited the large backlog but it didn't seem you inherited that degree of urgency to address the staffing shortfall."
Brazeau told the panel last week that it wasn't possible to estimate when the backlog will be cleared. She has hired an outside firm to develop a "productivity model" for the tribunal, Kenney told the committee hearing.
As of Thursday, the government had appointed 22 additional part-timers to help deal with the pileup of cases, Kenney said. The government has also shifted 12 members from the employment insurance section of the tribunal, with its manageable caseload, to the overtaxed CPP and old age security portion.
"We now have basically over 100 decision-makers working on the CPP side of the tribunal," he said, adding he's confident the backlog will soon start shrinking.
Earlier this month, the government also used its latest budget bill to remove a requirement in previous legislation to cap the size of the tribunal at 74 full-time staff. It also scrubbed limits on the number of hours part-time tribunal members are allowed to work.
Kenney says part of the reason for the backlog is because new tribunal members had to go through a 12-month screening process to ensure they were qualified.
"The reason we put in that rigorous pre-screening process .... is to make sure that we don't end up with unqualified patronage appointees," he said. Nonetheless, the Conservatives have appointed members to the new committee with ties to the party.
Allison Schmidt, a disability claims advocate based in Regina, Sask., said if it's true that a 12-month screening process has bloated the backlog, it's a problem the government brought on itself.
"There were 250 to 300 trained tribunal members under the former system," she said of the former office of the commissioner of the review tribunal.
"There was an extremely good knowledge base, a bank of well-qualified and experienced tribunal members from the previous system who provided Canadians with excellent service. But very few of these experienced members were reappointed to the new social security tribunal; I believe they were all dismissed."
Follow Lee-Anne Goodman on Twitter @leeanne25