NEW YORK (Bloomberg) — BlackRock Inc., the largest publicly traded US asset manager, pulled out of a $3.2 billion class-action settlement against Bermuda-based Tyco International Ltd. to pursue its own shareholder lawsuit.

BlackRock filed an "opt-out lawsuit" on January 29 against Tyco International and two spin-off companies, Tyco Electronics Ltd. and Covidien Ltd., Bermuda-based Tyco Electronics said today in a regulatory filing.

Tyco International won formal approval in December to settle investor claims that it inflated revenue during the tenure of former chief executive officer Dennis Kozlowski. The company agreed to pay $2.98 billion and PricewaterhouseCoopers LLC, Tyco's former auditor, agreed to contribute $225 million. New York-based BlackRock opted out of the agreement and filed its own suit against Tyco in January, the US Securities and Exchange Commission filing said.

"There's been the tendency of courts to limit class actions, but they can't limit the action by institutions, so it pays for them to opt out and file on their own," Tamar Frankel, a law professor at Boston University, said in an interview.

Former executives of Bermuda-based Tyco, the world's biggest maker of security systems, overstated income by $5.8 billion under Kozlowski. Shareholders claimed the company lost more than $100 billion in market value because of the fraud. Kozlowski was convicted of fraud and is serving an 8 ? to 25-year prison term in state prison in New York.

Tyco Electronics is responsible for 31 percent of the class-action settlement amount and any claims arising from opt-out lawsuits, according to the filing. Tyco International and Covidien are responsible for 27 percent and 42 percent, respectively.

Brian Beades, a spokesman for BlackRock, declined to comment. BlackRock, which oversees $1.4 trillion, owned 4.58 million shares of Tyco International, or 0.9 percent, as of December 31, data compiled by Bloomberg show. It owned 1.08 million shares of Tyco Electronics and 4.2 million shares of medical supplies maker Covidien.

Sheri Woodruff, a spokeswoman for Tyco Electronics, said the company was "aware there would be opt-outs", while declining to comment further on the lawsuit.

Bruce Farmer, a spokesman for Mansfield, Massachusetts-based Covidien, declined to comment. Paul Fitzhenry, a spokesman for Tyco International, wasn't immediately available to comment.