Seau committed suicide by a self-inflicted gunshot in May 2012. He was 43.
Seau's ex-wife and four children filed a lawsuit Wednesday claiming the football player's suicide was caused by brain disease, the result of violent hits sustained while playing professional football.
The National Football League committed "acts or omissions" hiding dangers of repetitive blows to the head, the lawsuit contends. The lawsuit was filed in California Superior Court in San Diego. Seau spent much of his career playing for the San Diego Chargers.
Helmet manufacturer Riddell Inc. was also named in the lawsuit. The Seau family claims the company was "negligent in their design, testing, assembly, manufacture, marketing, and engineering of the helmets" used by NFL players. The suit says the helmets were unreasonably dangerous and unsafe."
Tests performed on Seau's body show he was suffering from chronic traumatic encephalopathy (CTE), a brain injury.
The lawsuit accuses the league of glorifying the violence in pro football, and creating the impression that delivering big hits "is a badge of courage which does not seriously threaten one's health."
"Our attorneys will review it and respond to the claims appropriately through the court," the NFL said in a statement Wednesday.
Riddell issued a statement saying it is "confident in the integrity of our products and our ability to successfully defend our products against challenges."
An Associated Press review in November found that more than 3,800 players have sued the NFL over head injuries in at least 175 cases as the concussion issue has gained attention in recent years. The total number of plaintiffs is 6,000 when spouses, relatives and other representatives are included.
Seau was one of the best linebackers during his 20 seasons in the NFL, retiring in 2009.
The Associated Press contributed to this report.