European Union governments are expected to agree later on Thursday to put the National Iranian Tanker Company (NITC), Iran's biggest tanker company, back on a list of sanctioned firms, EU diplomats said.
The EU's second-highest court ruled last July there were no grounds to blacklist the NITC after the company contested the designation, but the EU said it would seek legal means to keep the company on the list of companies under asset freezes.
One of the diplomats, who spoke on condition of anonymity, said discussions on the NITC were being held in closed-door meetings and cited a deadline of 4 p.m. (1500 GMT) on Thursday for any member states to object to putting the NITC back on the list.
The sanctions - imposed in 2012 over Tehran's disputed nuclear programme - prohibited any trade between the EU, its companies and citizens, and NITC, including the provision of services such as insurance or banking.
The decision would come at a sensitive time in negotiations to resolve a 12-year standoff between Tehran and the West over its nuclear programme.
Diplomats stress the EU is not imposing fresh sanctions, only changing the criteria to make them legally watertight.
Under last year's accord between Iran and the United States, France, Germany, Russia,China and Britain, the Islamic Republic halted its most sensitive nuclear activity and took other steps in exchange for some easing of economic sanctions.
