President Donald Trump’s firing of the former chairwoman of the National Labor Relations Board was an “illegal act,” a federal judge ruled Thursday, overturning her ousting in a decision that was highly critical of Trump’s “intent on pushing the bounds of his office.

A judge's ruling reinstating NLRB board member Gwynne Wilcox sets the stage for a battle over the agency's future, which could end up at the Supreme Court.

The ruling, which the Trump administration immediately moved to appeal, was a rebuke of Mr. Trump’s expansive view of executive power.