The companies are from China, India, and Austria. The sanctions are based on the Iran Non-Proliferation Act of 2000.
The legislation was enacted to help stop foreign transfers to Iran of weapons of mass destruction, missile technology, and advanced conventional weapons technology.
If found in violation, a company can face sanctions forbidding it from doing business with the U.S. government and U.S. companies.
Some 40 companies have been sanctioned since the legislation was enacted.