The federal government's bug-addled public service pay system saw a fresh spike in problems last month, the result of new labour contracts and summer hiring, officials said Friday.

Public Services and Procurement Canada managed to stabilize the backlog of pay change files that were being dealt with in March and April, deputy minister Marie Lemay told a teleconference.

But the backlog surged by about 10 per cent last month when the Phoenix system was inundated with new pay requests, she said.

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The system was jammed by pay changes made to accommodate new collective agreements coming into force for roughly 24,000 government employees working as financial managers, auditors, scientists and patent examiners, among others.

In addition, about 5,000 summer students were hired.

There are roughly 345,000 pay change transactions currently in the system, about 265,000 more than the system's average monthly capacity of about 80,000, officials said.

"All this means the number of transactions awaiting processing has grown," said Lemay.

At least one union representing civil servants predicted the backlog could grow larger still as new collective agreements come into force.

"The government should have foreseen this challenge months ago," said Steve Hindle, vice-president of the Professional Institute of the Public Service of Canada.

"The number of pay transactions resulting from implementation of new collective agreements is only going to increase over the coming months."

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The government said last month it was hoping to enlist 200 temporary workers on top of the 300 hired to date to deal with the Phoenix issues, which initially left tens of thousands of public servants underpaid, overpaid or not paid at all.

Lemay said Friday she expected up to 230 new pay system employees could be hired over the next two years, 90 of them at the government pay centre in Miramichi, N.B.

"We need the capacity," said Lemay. "It absolutely will help us get through that queue."

How long it will take to tame the backlog will depend on how quickly the department can hire — and train — new compensation advisers, said Lemay, noting that intensive "boot camp" training sessions were underway for the latest new hires.

The government said it will spend $142 million in hopes of bringing the Phoenix system to what it calls a "steady state."

The Liberals blamed the expense on the Conservatives, who they said axed hundreds of workers who handled pay claims before Phoenix was brought on line.

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"The previous government eliminated over 700 compensation jobs in departments, resulting in a shortage of capacity to implement a new pay system," said Steven MacKinnon, the parliamentary secretary to Public Service and Procurement Minister Judy Foote.

"We inherited this mess, but we are committed to fixing it."

Had those jobs not been eliminated, the pay system problems could have been significantly reduced, Lemay suggested.

"As part of the consolidation of compensation advisers in Miramichi, we lost experienced experts before Phoenix was launched," she said.

"We can now clearly see that this caused a critical gap during our transition to the new pay system. Having that expertise available during the implementation would have been a game changer."

The Conservatives, however, argued the Liberals knew of the pay system problems before deciding to launch Phoenix, and certainly had time to beef up staffing levels to cope with recent changes in civil service contracts.

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"It's stunning that the deputy minister said her department was unprepared for things like summer students and new collective agreements, even though these factors had been anticipated for over a year," said Conservative public service deputy critic Kelly McCauley.

"The Liberals have mismanaged the Phoenix pay fiasco from Day 1 and taxpayers are going to be forced to pay for their mistakes."