A U.S. hedge fund, Steelhead Partners LLC, has become AbitibiBowater's biggest shareholder.

Steelhead has tripled the amount of shares it owns in recent weeks, and now owns 14.8% of AbitibiBowater's shares.

An AbitibiBowater spokesman said the company was unaware of Steelhead's involvement.

Steelhead is known for its aggressive stance toward management. Steelhead's presence could increase the pressure on AbitibiBowater to raise cash quickly.

AbitibiBowater is currently scrambling to refinance or repay more than $700 million (U.S.) that is due this year.

AbitibiBowater has a non-binding agreement to sell its lucrative Ontario hydro stations to a unit of Toronto-based Brookfield Asset Management Inc in an attempt to liquidize assets to make their debt payments.

But sources are saying that AbitibiBowater have been stalling in order to get a higher price for the hydro plants.

AbitibiBowater currently holds more than 40% of the North American newsprint market.

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