WASHINGTON (Reuters) - The Senate is looking to strengthen the economic chokehold on Iran with even stricter measures to cripple Tehran's oil revenues and possibly its shipping in legislation that is expected in the coming weeks.
Lawmakers want to move quickly to constrict the funding that Western nations suspect Iran is using to develop nuclear weapons.
The sanctions, still in draft form, would follow legislation passed in December and seek to capitalize on moves by the European Union toward an Iranian oil embargo and sanctions against Iran's central bank.
Details may be unveiled in the Senate Banking Committee as early as next week after members return to Washington from a winter recess. But action could slip into February, Capitol Hill aides told Reuters.
One congressional aide said senators were discussing provisions that would make President Barack Obama decide whether to blacklist Iran's oil tanker operator, the National Iranian Tanker Company (NITC), and the National Iranian Oil Company (NIOC).
The idea is to give Obama a deadline to determine whether Tehran's tanker operator and oil company have any links to Iran's Revolutionary Guards Corps.
The congressional aide, who asked not to be named, said the time frame for the president to make a decision would be around 60 days so the administration "can't sit on it. They would have to make a determination."
Another lawmaker's aide said the bill being drafted may include measures that would sanction foreign entities that buy oil from affiliates of Iran's Revolutionary Guards Corps.
A committee aide confirmed that the banking panel's chairman, Democrat Tim Johnson, was working on a bipartisan Iran sanctions bill with the ranking Republican, Richard Shelby. Committee aides declined to provide details.
The proposed measures come as the Obama administration struggles to implement sanctions on foreign banks handling Iranian oil transactions that became law on December 31.
The challenge for the administration, with an eye toward the November elections, will be to implement the rules without driving oil prices higher and hurting the fragile U.S. economy.
Senators Robert Menendez and Mark Kirk warned Treasury Secretary Timothy Geithner this week that they would be watching closely to make sure countries were not allowed to escape financial sanctions.
A Treasury Department official declined comment on actions the U.S. government may or may not take.
"The NITC and NIOC already fall under U.S. sanctions and we continue to work with the international community to further increase the pressure on Iran to deepen the impact through the application of appropriate sanctions and calibrated efforts to reduce Iran's oil revenues," the Treasury official said.
The new sanctions package could include some tweaks to the law passed late last year, one Capitol Hill aide said.
Bills slapping new sanctions on Iran attracted broad support in the Senate and House of Representatives last year, making it one of the few issues to sail through the otherwise gridlocked U.S. Congress.
On December 14, the House passed legislation similar to what is now being readied in the Senate, expanding oil-related sanctions on Iran and closing loopholes.
"We just need to pass this bill, we passed it in the House overwhelmingly," Ileana Ros-Lehtinen, who led House efforts on the sanctions, told reporters this week. Some of the Senate provisions were introduced months ago but have not seen action, she noted.
The bill emerging in the Senate Banking Committee is expected to have in play provisions requiring foreign companies to disclose business done with Iran in their mandatory filings with the U.S. Securities and Exchange Commission.
That provision, as well as sanctions on foreign companies that buy oil from Revolutionary Guards Corps affiliates, was part of a Senate bill first introduced by Menendez in May 2011.
Senators continue to mull how to deal with ideas that may be out of the Banking Committee's jurisdiction, such as some affecting shipping. Those items could be acted on at a later point in the legislative process, aides said.
An aide to Senator Kirsten Gillibrand said the New York lawmaker hopes to include some sanctions on Syria. Those sanctions may be viewed as connected to the Iranian issues because of Syria's close ties to Tehran, the aide said.
Sanctions on shipping companies that have visited Iran, North Korea or Syria in the previous 180 days - a measure originally included in the Menendez bill and expanded upon in the House-passed legislation - may be out of the Banking Committee's jurisdiction, two Senate aides said.
Also beyond the scope of the banking bill may be a package of human rights sanctions on foreign companies that sell "tools of oppression" to Iran - items used to kill, torture or oppress citizens.
Congress is also considering measures that would see the U.S. government ban shipping classification societies from providing services to vessels in the United States if they also provide those services to vessels for Iran, North Korea, Sudan or Syria.
Without certification by a classification society, shippers would find it difficult to get insurance or enter major ports.
In November the Senate Commerce Committee approved the measure, introduced by Susan Collins, Joe Lieberman and Mark Begich, as part of a Coast Guard bill. It could be voted on by the Senate in coming months, a Senate aide said.
Additional reporting by Susan Cornwell; Editing by Russell Blinch