The Superfund excise tax is imposed by section 4661 of the Internal Revenue Code (IRC) on the sale or use of certain chemicals and petroleum products. The tax is designed to fund the cleanup of hazardous waste sites under the Superfund program.

If a US company has a maquiladora subsidiary (a manufacturing operation in Mexico that is owned and operated by a foreign company), it may still be subject to the Superfund excise tax if it produces or uses certain chemicals and petroleum products that are subject to the tax.

Section 4672 of the IRC provides that the Superfund excise tax is imposed on the sale or use of taxable chemicals and petroleum products by the manufacturer, producer, or importer of the products. Therefore, if the US company or its maquiladora subsidiary is the manufacturer, producer, or importer of the taxable chemicals and petroleum products, it may be subject to the Superfund excise tax.

It's important to note that the Superfund excise tax applies to specific chemicals and petroleum products that are listed in the IRC. The list includes a range of chemicals and petroleum products, such as crude oil, gasoline, diesel fuel, and certain chemicals used in manufacturing processes.

If you believe your company may be subject to the Superfund excise tax, it's best to consult with a tax professional who can provide guidance specific to your situation.