NFL gets tougher on domestic violence

• NEW: Players union says it will continue to defend players rights


• The new policy takes effect immediately, NFL Commissioner Roger Goodell says


• The commissioner admitted he should have punished Ray Rice more severely


• Rice got two-game suspension after video showed him dragging his now-wife

(CNN) -- In the wake of criticism over a two-game suspension for Baltimore Ravens running back Ray Rice, the NFL has established a six-game unpaid ban for personnel who violate the league's policy on domestic violence, Commissioner Roger Goodell said Thursday.

A second incident would be punished by a lifetime ban from the league, Goodell said in a letter and memo to the owners of the league's 32 teams.

Without referring to Rice by name, he acknowledged in his letter that he made the wrong decision in that case.

"I didn't get it right. Simply put, we have to do better. And we will," he wrote.

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The policy, which is effective immediately, also applies to other types of violence.

"Violations of the Personal Conduct Policy regarding assault, battery, domestic violence or sexual assault that involve physical force will be subject to a suspension without pay of six games for a first offense, with consideration given to mitigating factors, as well as a longer suspension when circumstances warrant."

Goodell said the circumstances that would warrant a longer suspension include incidents that predate a person's time with an NFL team or acts that involve choking, repeated blows or a weapon. They also include violence against a pregnant woman or in view of child.

Lifetime bans may be appealed after a year.

The players union issued a response.

"We were informed today of the NFL's decision to increase penalties on domestic violence offenders under the Personal Conduct Policy for all NFL employees. As we do in all disciplinary matters, if we believe that players' due process rights are infringed upon during the course of discipline, we will assert and defend our members' rights," the NFL Players Association said in its statement.

Read the letter and memo

Rice was suspended for two games after video showed him dragging his unconscious fiancee -- whom he later married -- from an elevator.

Rice resolved the charges stemming from the incident with his now-wife, Janay, and entered a pretrial intervention program in May, the NFL said. Under the program, he won't be prosecuted, and the charges will be expunged after a year, the league said.

The punishments, both from the NFL and from the criminal justice system, were widely decried as too light, and the issue quickly spiraled into debates over domestic violence and victim-blaming.

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Goodell's letter tells teams to distribute a memo about the new policy to each player and all members of the organizations.

The NFL's Personal Conduct Policy states that employees are "held to a higher standard" of conduct.

"Persons who fail to live up to this standard of conduct are guilty of conduct detrimental and subject to discipline, even where the conduct itself does not result in conviction of a crime," the policy states.

The NFL regular season is 16 games.

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CNN's Jason Durand contributed to this report.