Japanese news media are reporting that the country's major oil wholesalers are preparing to suspend crude imports next month.
Jiji Press agency and Kyodo on September 3 reported that the action comes in response to U.S. sanctions against Tehran and threats they could be extended to companies doing business with Iran.
U.S. President Donald Trump in May pulled out of the 2015 nuclear deal with Iran and almost immediately began reimposing sanctions against Tehran.
Washington has said it will reimpose sanctions on Iran's oil exports and banking sector in early November, with the goal being to bring other countries' imports of Iranian oil down to zero.
Jiji Press said it appeared Japan will be unsuccessful in its efforts to get a waiver from Washington that would allow it to continue importing oil from Iran.
That has forced Japanese oil companies to prepare to suspend Iranian imports and look for ways to switch to other Middle East producers, Japanese media report.
A Trade Ministry official confirmed to AFP that Japan had requested a waiver but declined to comment further.
A spokeswoman for crude wholesaler Showa Shell Sekiyu told AFP that the company will "observe a government decision" on Iranian oil imports but would not provide specifics.
Other wholesalers declined to comment.
Japan is reliant on outside sources for energy, importing 80 percent of its oil from the Middle East in recent years.
The Japanese government said Saudi Arabia is Japan’s largest supplier of crude at 39 percent. Iran is sixth at about 5 percent.
In August, Iran's oil minister said that French oil-and-natural-gas company Total had "officially left" Iran in the face of the U.S. threats.
U.S. sanctions have had a major impact on Iran's economy, leading to public discontent and putting pressure on President Hassan Rohani's government.