The exodus of partners from national law firm Heenan Blaikie LLP shows no sign of slowing, as a senior employment lawyer jumped ship to a rival on Thursday ahead of a key partners' meeting on the weekend to hash out the firm's future.

The departure of Toronto-based Tim Lawson – a member of Heenan Blaikie's executive committee with 20 years at the firm – for McCarthy Tétrault LLP is the latest in a wave of more than 30 partners who have left since 2012 amid an industry-wide dearth of mining and resource merger deals. Mr. Lawson said on Thursday he could not comment on his former firm.

Heenan Blaikie has previously acknowledged that the past year has been challenging financially and has said it is going through a "strategic review," prompting many of the departures. It has also said that out of financial prudence, it delayed certain payments to partners last year, but has since paid out much of the money owed.

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In the last few weeks, Heenan Blaikie – which is home to more than 500 legal professionals, including former prime minister Jean Chrétien – has seen at least five partners leave.

In an e-mail, national co-managing partner Kip Daechsel declined to comment, saying the firm's partners were busy preparing for their previously scheduled retreat this weekend.

Toronto partner Norman Bacal, who was managing partner until 2012, said in an e-mail that he had no comment until next week, "at which point I will be happy to share my views with you."

At the retreat, the firm's partners are expected to consider options for the future, including pursuing a merger with a global law firm, according to a source. Some legal industry observers on Bay Street have speculated the firm might break up or shrink. Others suggest the firm will weather the storm.

Heenan Blaikie, which has nine offices across Canada and opened a Paris branch in 2011, is not the only major Canadian law firm in a slump, as the volume of mergers and other corporate deals has slowed. But it is going through the most dramatic wave of departures from a Canadian law firm since the collapse of Toronto mid-sized firm Goodman & Carr in 2007, which shrunk dramatically from 140 to just 90 partners in the face of increasing economic pressure before shutting down.

In an interview earlier this month, Mr. Daechsel said Heenan Blaikie was financially sound but was "right-sizing," although he acknowledged some of the lawyers who left were ones the firm wanted to keep. He also stressed that the firm had recently hired about 20 lawyers, including seven with the rank of partner or counsel. He said billing levels were "much more encouraging" since November, and dismissed rumours the firm could collapse.

Heenan Blaikie has been spending money on renovating its Montreal and Vancouver offices and moving into new quarters in Sherbrooke, Que. And almost five years ago, its Toronto office moved into state-of-the-art premises in the city's sleek new Bay Adelaide Centre, signing what the firm said at the time was a "long-term lease" on five floors in the 51-storey building, where fellow law firms Fasken Martineau DuMoulin LLP and Goodmans LLP are also now located.

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Heenan Blaikie's history dates back to 1973, when Montreal lawyer Donald Johnston – later a Trudeau cabinet minister and secretary-general of the Organization for Economic Co-operation and Development – formed the firm with Roy Heenan and Peter Blaikie.