".. Proliferation-sensitive equipment & materials to Iran by Chinese companies.."

"..."It appears that Chinese firms in the energy and banking sectors have conducted significant activity in violation of U.S. law," the senators stated. "We cannot afford to create the impression that China will be given free rein to conduct economic activity in Iran when more responsible nations have chosen to follow the course we have asked of them. We are sure you agree."......

One of the main concerns on Capitol Hill is that as countries pull out from Iran, other countries will take over contracts, thereby nullifying the effect of the sanctions -- a practice known as "backfilling." For example, the administration and Congress worked hard to convince Japan and South Korea to impose unilateral measures against Iran. However, there's particular concern that China firms will simply come in and take over those contracts. ..."