A federal court Wednesday allowed a handful of states controlled by Democratic administrations to help defend the Obama administration’s ozone pollution rule in an ongoing lawsuit.

The decision by the Court of Appeals for the District of Columbia Circuit means California, New York, Vermont, Washington, Delaware and the District of Columbia can be more closely involved in defending the 2015 Environmental Protection Agency (EPA) regulation.

The states, led by California, had asked the court last month to let them become intervenors in the case. They were previously amici, a position that lets them file briefs but doesn’t allow them to be active parties in the litigation with the right to appeal.

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The case began in 2015, when industry groups and states with conservative administrations challenged the EPA’s regulation limiting the allowable level of ozone pollution to 70 parts per billion, from 75.

The Trump administration is in the process of deciding whether it wants to change or repeal the regulation.

The EPA and the groups and states challenging the rule had fought the motion filed by Democratic attorneys general and asked the court to deny it.

In June, EPA head Scott Pruitt delayed compliance with the rule by a year, an action that Democratic attorneys general challenged Tuesday in a separate lawsuit.

Wednesday’s action by the D.C. Circuit court means that if the EPA decides not to defend the ozone rule, the states could carry on with the case themselves.