Fiat, which supplies complete knock down (CKD) car kits to Iran Khodro, has used Lopez in a series of high profile - and controversial - TV and print ads.
The advocy group, United Against Nuclear Iran (UANI) says that it has been contacting Fiat representatives for nearly a year about its concern with the Italian brand's ties to the Middle Eastern country.
"Giving the high profile endorsement contract that Ms. Lopez has with Fiat, we've decided to contact her and seek her help in pressuring Fiat to end their business in Iran,"ť UANI communications chief Nathan Carleton told Fox News.
UANI has also tried to directly contact Lopez in a letter that has been published online, but the group says it is waiting until this week to increase pressure on both the pop star and the automaker.
UANI, founded by former American diplomats including former U.S. Ambassador to the United Nations Richard Holbrooke, says that its mission is to help prevent "Iran from obtaining nuclear weapons."
"We think her fans will appreciate such a prominent person take a stand against these human rights violations that Fiat is contributing to,"ť Carleton said.
The Fiat ads, which promote the minicar's return to the North American market through Fiat subsidiary Chrysler's network, have come under fire several times before. Lopez, who gained early attention for her song "Jenny from the Block," was not on site in New York's Bronx borough during filming, so a body double was used, and a group of muralists sued the automaker for using their "I Love the Bronx" mural without permission.