Solomon Technologies filed a complaint with the panel last month saying the hybrid transmission in the two popular vehicles infringed its patent related to motor and transmission systems.
If the ITC agrees with Solomon, Japan's top auto maker could be banned from importing the systems and the Prius and Highlander hybrid models that they power. The ITC said opening a case does not mean it has made any decision on the merits.
A Toyota spokesman said it cannot comment on ongoing cases.
In September, Solomon applied to a Florida federal district court for an injunction against Toyota barring infringement and damages for unauthorized use of its patented technologies.
Toyota sold 110,000 Prius models and 18,800 Highlander hybrid SUVs in North America last year.