WASHINGTON -- Alarm bells rang in the auto enthusiast community last week after a trade group warned that the EPA was threatening to ban the type of modified street cars that generations of amateur racers have taken to the track.

Relax, the EPA said. There's no new ban being proposed. Fact is such modifications have always been banned under the Clean Air Act.

So what is going on?

Call it a muddled exchange that nonetheless sheds light on one of the EPA's enforcement priorities in the context of Volkswagen's diesel transgressions. In short, the EPA's concern is not about the emissions of race cars but about keeping all road-going cars free of modifications that would neuter their emissions controls.

Adam Kushner, a partner at the law firm Hogan Lovells and former enforcement official at the EPA, says it should be no surprise these days that regulators are scrutinizing how emissions-control systems are being modified in the new-vehicle and aftermarket sectors.

"The regulated community is going to need to be watchful," said Kushner, who was director of the EPA's Air Enforcement Division from late 2003 to late 2008 and director of its Office of Civil Enforcement from late 2008 to late 2011.

The EPA proposal that sparked last week's controversy seeks to add language to a "prohibited acts" section of existing light-vehicle regulations saying certified motor vehicles and their emissions components "must remain in their certified configuration even if they are used solely for competition or if they become nonroad vehicles or engines."

The EPA's addition was tucked inconspicuously into the agency's 629-page proposal to set 2021-27 medium- and heavy-vehicle greenhouse gas targets. It was published in the Federal Register in July 2015. The EPA is expected to issue its final rule for the big truck standards in July and is still considering comments from the public.

The disputed language was meant to clarify that a separate exemption for "nonroad" vehicles, such as all-terrain vehicles, snowmobiles and dirt bikes, didn't extend to motor vehicles, according to Laura Allen, the EPA's deputy press secretary.

Yet it was seized on by the Specialty Equipment Market Association, which last week warned that the rule would expose racers and some aftermarket companies that serve them to penalties and reverse decades of agency policy on the issue.

"This is a change of heart in terms of their interpretation of the law," said Steve McDonald, SEMA's vice president of government affairs.

That's not the case, according to the EPA. While the agency has long had a rule on its books against tampering with the emissions controls on light-duty vehicle engines -- that is, prohibiting the very thing that many racers do to extract more power from their track cars -- the rule has never been an enforcement priority. The agency's de facto posture is: Let racers race.