As the August 1 deadline for trade deals or sweeping tariffs on countries around the world nears, and the Trump administration advises the market “not to panic,” wholesalers and distributors are warning of a massive hit to a sector at the heart of the U.S. economy.

Wholesalers and distributors account for approximately one-third of gross domestic product across all of the goods and services they handle, according to Eric Hoplin, president & CEO of the National Association of Wholesaler-Distributors, and he says the $8.2 trillion industry will suffer the biggest blow from President Trump’s trade policy.

Companies in this segment range in size from small family businesses to Fortune 500 companies, with the smaller firms expected to face greater financial pressures.

The top five wholesale product categories include healthcare goods, food, clothing, building materials, and technology, but the goods and services handled range much more widely, from oil and gas to industrial products, motor vehicles and auto parts, commercial equipment and supplies, office products and paper merchants, furniture and home furnishings, chemicals and plastics, apparel, alcoholic beverages, hardware, plumbing and heating, agriculture products, and a wide range of durable goods and consumer products.