It looks as though the “super PAC” era is coming to New York.

A federal appeals court on Thursday ruled that a conservative group supporting Joseph J. Lhota, the Republican nominee for mayor of New York City, can immediately begin accepting contributions of any size because New York State’s limit on donations to independent political committees is probably unconstitutional.

The ruling, 12 days before the mayoral election, is not likely to change the dynamics of the race, given the wide lead of the Democratic candidate, Bill de Blasio, and a presumed reluctance by many potential big donors to donate to an underdog candidate this late in the game.

But an end to limits on contributions to independent political groups could have a much bigger impact next year, when voters will decide whether to re-elect Gov. Andrew M. Cuomo, a Democrat, and will determine which party controls the State Senate — a long-running battle in which independent spending could make a significant difference.

“This could usher in an era where super PACs call the shots in campaigns all over the state, not just in the city,” said David Donnelly, the executive director of the Public Campaign Action Fund, which advocates public financing of elections.