Automakers and their dealers have millions of reasons to be concerned about weakening U.S. new-vehicle sales — nearly 4.2 million reasons, to be more precise.

As reported by Automotive News, that’s how many unsold cars and trucks the industry had on hand going into this month, an unwieldy pool of vehicles that has spilled into vast overflow lots popping up wherever enough wide-open space is available: shuttered factories, vacant shopping centers, barren fields.

The estimated 4,188,200 unsold vehicles on April 1 was the highest inventory number for any month since that reported for July 1, 2017, and just 114,300 vehicles less than the modern-day record set in May 2004, according to the Automotive News Data Center. It’s over half a million vehicles more than automakers and dealers were grappling with in the spring of 2007, when the Great Recession was just around the corner. The figures do not include the estimated 18,000 electric vehicles that Tesla had in inventory this month.

Bulging inventories, combined with rising floorplan interest rates, are sapping whatever was left of dealers’ new-vehicle margins and threaten to unravel the industry’s hard-fought pricing discipline if demand erodes further.

Pushed each month by factory reps to load their lots with more and more of the latest and greatest, many dealers now find themselves stuffed to the gills, paying extra for off-site storage while the interest clock ticks and each vehicle’s floorplan allowance melts away.

“I know my customers have a problem when they don’t have room to park the cars,” said Carl Woodward, a longtime certified public accountant in central Illinois who provides accounting services to more than 250 dealerships in 18 states.

Dealers can take comfort that U.S. sales are still relatively strong. But there are also clear signs that the industry, after rising in eight of the last nine years, has passed its peak for this cycle. Sales were down 3.2% in the first quarter of 2019, which analysts say is likely to be the first year since 2014 that falls short of 17 million vehicles.

The situation is admittedly less dire than in the run-up to the last recession, with consumer confidence remaining healthy, automakers generating solid profits and more flexible union contracts affording the Detroit 3 greater control over production today. But the problem has caught some dealers off guard because of how quickly the cost to carry today’s inventory — largely high-priced pickups, SUVs and crossovers — has risen, as floorplan interest rates surged from a comfortable 1.5% only a few years ago to more than 5% now.

And if a downturn comes, dealers sitting on big inventories could find themselves in a great deal of trouble.

“Right now, there’s excessive inventory out there, and there’s a tremendous amount of pressure from almost all the brands to take additional cars,” David Hult, CEO of Asbury Automotive Group Inc., told Automotive News last week after reporting the dealership group’s first-quarter earnings.