US President Barack Obama has scrapped proposals to tighten rules on air pollution.
He has ordered the Environmental Protection Agency (EPA) to shelve plans to reduce concentrations of ozone - one of the main contributors to smog.
Mr Obama said he was pulling the measure as part of a government effort to reduce regulatory burdens and uncertainty as the economy struggles.
Businesses have said the measure would cost them billions of dollars and kill jobs.
Business groups and Republican politicians welcomed the decision, but environmentalists condemned it, with one of them saying it was a huge win for corporate polluters and a huge loss for public health.
The EPA had estimated that the new rules could have saved as much as $118 billion in health costs, and helped prevent as many as 12,000 premature deaths from heart and lung complications.
Ozone is a lung irritant, connected with asthma and other respiratory conditions.
