According to official information, a "technical defect" paralyzed the payment system at Iran's gas stations across the country.
"In the morning we got the message that because of a software defect, refueling with the subsidy card is no longer possible in many petrol stations across the country," said a spokesman for the petrol station association on Tuesday, according to the Isna news agency.
This means that Iranians can only fill up without this fuel card, but the fuel is then twice as expensive.
Eyewitnesses reported that long lines formed in front of gas stations in the capital Tehran.
State television later confirmed the manual sale of gasoline without a card was not affected.
As long as the card-based system is suspended, drivers would have to pay a more expensive, non-subsidized tariff.
Who is behind the attack?
Since the problem could not be resolved even after several hours, speculation circulated on social media about a cyber attack by Israel on the software of the payment system of the petrol stations.
Israel has carried out several cyber attacks on the Iranian nuclear organization's network over the past few years, causing significant financial damage.
Bloomberg again quoted the Fars news agency that the disruption may be related to the upcoming anniversary of the violent protests in 2019.
At the time, demonstrations had broken out across the country after the government drastically increased fuel prices.