A lawsuit has been filed against the insurer that wrote Heath Ledger's $10 million life insurance policy challenging the company's claim that the actor's death in January 2008 may have actually been a suicide.

In court papers obtained by ET, the lawsuit claims the insurer, ReliaStar, acted in bad faith and engaged in the "illegal and unfair practice" of post-claim underwriting by insisting the deceased actor may have committed suicide even though his death was officially ruled an accidental overdose.

When Ledger took out the policy in 2007, he named his daughter, Matilda Rose, who turns three next month, as the sole beneficiary. Lawyers filed the lawsuit on his behalf in Los Angeles Superior Court this month.

Investigators concluded that Ledger died of an accidental overdose of drugs at his New York apartment in January 2008.

In ReliaStar's answer to the complaint, the company asserts that it "is entitled to investigate plaintiff's claim to determine if the 'suicide' provision is applicable."

One of the attorneys working on behalf of Matilda's estate, William Shernoff, said the insurance company is just trying to keep the case tied up in court to avoid paying the benefit. "ReliaStar is just trying to drag out the process, for what could be years, to avoid paying the money," Shernoff said.

According to Shernoff, ReliaStar's lawyers have informed Matilda's attorneys that as part of their investigation, they intend to take the depositions of actress Mary-Kate Olsen, the masseuse who was at Ledger's home when he died, as well as Ledger's colleagues on his last film, his agents, doctors, psychologists and others.