(Reuters) - Actor and comedian Tracy Morgan and others in his limousine were not wearing seat belts when their vehicle was struck by a Wal-Mart truck in a June highway accident, the retailer said on Monday.

Wal-Mart Stores Inc made its contention in a court filing responding to a lawsuit by Morgan and three other plaintiffs over the crash on the New Jersey Turnpike.

Known for his work on NBC's "30 Rock" and "Saturday Night Live," Morgan spent several weeks in rehabilitation following the June 7 accident, which killed his friend and fellow comedian James McNair.

In its filing, Wal-Mart said the injuries suffered by surviving passengers were caused in whole or in part by their "failure to properly wear an appropriate available seatbelt restraint device."

Wal-Mart said that by failing to use seat belts, the passengers "upon information and belief, acted unreasonably and in disregard" of their best interests.

Other plaintiffs include comedian Ardley Fuqua Jr, Morgan's assistant Jeffrey Millea and Millea's wife, Krista Millea.

"It's not a defense. They're trying to mitigate their damages," Benedict Morelli, a lawyer for the plaintiffs, said in a phone interview.

"Any time a lawyer says 'upon information and belief,' it means they don't know," he added. "Maybe they want to play hardball. If so, I'm ready."

In their July 10 lawsuit, the plaintiffs claimed that Wal-Mart knew or should have known its truck driver, Kevin Roper, had been awake for more than 24 hours before the crash, which under the law meant he should not have been on the road.

Federal investigators have said Roper was driving roughly 20 miles per hour (32 km per hour) over the speed limit just before the crash.

Wal-Mart spokeswoman Brooke Buchanan said the company remains "willing to work with Mr. Morgan and the other plaintiffs" to resolve the lawsuit.

Wal-Mart has said it was sorry that one of its trucks was involved. The Bentonville, Arkansas-based retailer declined in its filing to address many of the plaintiffs' claims, citing a pending probe by the National Transportation Safety Board.

Roper has been charged with vehicular homicide and assault-by-auto and pleaded not guilty.

(Reporting by Jonathan Stempel in New York; Editing by Cynthia Osterman and Lisa Shumaker)