The federal appeals court in Washington began hearing oral arguments Tuesday in the legal fight over President Barack Obama's plan to curtail greenhouse gas emissions.

The Clean Power Plan, which aims to slow climate change by reducing power-plant emissions by one-third, has been challenged by more than two dozen mostly Republican-led states, including Texas, and allied business and industry groups tied to fossil fuels. The states deride the carbon-cutting plan unveiled by the Environmental Protection Agency as an "unlawful power grab" that will kill coal-mining jobs and drive up electricity costs.

The Supreme Court has delayed implementation until the legal challenges are resolved.

Implementation of the rules is considered essential to the United States meeting emissions-reduction targets in a global climate agreement signed in Paris last year. The Obama administration and environmental groups also say the plan will spur new clean-energy jobs.

Regardless of which side prevails at the appeals level, the issue is considered likely to end up being decided by the Supreme Court.