President Obama was bombarded by nearly 300 groups representing business and manufacturers on Wednesday, urging him to scrap new rules for reducing smog-forming ozone as the costliest regulations in history.

"The need for balanced government policies and reasonable flexibilities has never been greater, and no single regulation threatens to disrupt this balance more than EPA's ozone rule," the groups told the president in a letter sent to the White House.

The National Association of Manufacturers, the Business Roundtable and the U.S. Chamber of Commerce — the largest business lobbies — sent the letter to Obama, signed by 260 other trade organizations, one day after kicking off a major ad campaign to raise awareness of the harmful effects of the regulation.

The manufacturers started the multi-million dollar ad campaign on Tuesday, targeting lawmakers before they adjourn for the August congressional recess. The campaign is part of an eleventh-hour lobbying blitz against the proposed rules before they go into effect Oct. 1.

"In the coming weeks, the Environmental Protection Agency (EPA) will send your Office of Management and Budget a new National Ambient Air Quality Standard (NAAQS) for ozone that will be among the most expensive regulations in our nation's history," the letter reads. "Just a few years ago, you ordered the EPA to abandon a similar rule, citing the need to reduce regulatory burdens in a recovering economy. The undersigned organizations request that you do so again."

The letter follows similar messages sent to the White House in recent months by the attorneys general of nearly half of the states, decrying the rule as impossible to achieve.

The business groups want the president to keep in place the current air quality standards that states still are trying to reach. The current 2008 rules set a standard of 75 parts per billion for reducing ozone emissions. But the new EPA proposal would ratchet that down to as low as 65 ppb, which would place most of the national parks and areas of pristine wilderness out of compliance.

The groups' "simple, but critical request" is clear: "Please retain the existing 75 parts per billion (ppb) standard for ground-level ozone. Let us meet these requirements before moving the targets again," the letter says.

The manufacturers' ad blitz underscores the "absurdity" of the rules, driving home the point that if Yosemite can't comply, what hope is there for most of the cities and rural areas of the United States to meet the standards.

The entire country would be out of compliance, they argue. On top of that, a study the manufacturers had done shows that the rules would cost the economy nearly $140 billion a year.

"We are committed to ensuring a clean and safe environment now and in the future," the letter reads. "However, we also stand to bear the brunt of the economic pain from a regulation that will make it difficult to manufacture products, build new projects, produce energy, improve infrastructure and hire the workers needed to make this all happen."