The Obama administration is pressing Congress to exempt certain companies from possible sanctions directed at Iran, a move one lawmaker said is aimed squarely at letting businesses in China and Russia off the hook in exchange for their cooperation. 

Lawmakers from the House and Senate are negotiating on a bill that would penalize companies for doing business with Iran's energy sector. The administration is lobbying for an exemption for companies based in "cooperating countries" -- presumably meaning countries cooperating with the Obama administration's Iran strategy. 

The effort, first reported by The Washington Times, is not sitting well with some in Congress. Rep. Ileana Ros-Lehtinen, R-Fla., said the exemption clearly is aimed at Russia and China, which have business ties to Iran and which the Obama administration needs to pass U.N. sanctions on the Islamic republic. 

"The security of our nation and our allies cannot afford... to produce a bill that is so full of holes," Ros-Lehtinen told Fox News. "It is time for Congress to fill the vacuum created by executive branch inaction ... and enact crippling, mandatory sanctions that address the rapidly growing threat posed by Iran." 

House and Senate lawmakers are set to meet in a conference committee Thursday to try to hash out the details of a final bill, which they hope to complete by next month. It coincides with U.S.-led negotiations on a fourth round of U.N. sanctions against Iran, intended to halt uranium enrichment. 

But a senior Obama administration official told Fox News that it is working toward "the toughest possible" U.N. sanctions and disputed the idea that it was trying to water down the congressional legislation. 

"We're also involved in conversations with Congress about sanctions legislation to ensure it has sufficient breadth and depth. We strongly reject the idea that it's somehow being weakened," the official said. "Rather, we're working to make sure the president has the maximum amount of flexibility as we increase the pressure on Iran across many fronts. The exemptions discussed are not targeted to any country in particular, but would be based on objective criteria and made in full consultation with Congress." 

Meanwhile, Iranian President Mahmoud Ahmadinejad has applied for a visa to attend a nuclear summit at the United Nations next week, an opportunity for him to lobby world leaders against the sanctions.