Indeed, according to a statement from CSPI, both Burger King and Wendy's are still serving fries containing more trans fats than exceeds the daily recommended amount.
"French fries are fried twice, once in the factory and once in the restaurant," said CSPI executive director Michael Jacobson.
"If these chains want to claim they are switching to trans-fat-free frying oil, they need to switch it at the supplier as well as at the restaurant.
Burger King and Wendy's are really deceiving consumers with the public statements they've made about trans fat, which don't tell the whole story."
New York City introduced a ban on the use of trans fats in restaurants in September last year.
The restaurants were given six months to switch to oils, margarines and shortening used for frying and spreading that have less than 0.5 grams of trans fat per serving.
After 18 months, all other food items - including all margarines and shortenings - must contain less than 0.5 grams of trans fat per serving.
The CSPI reportedly surveyed large orders of French fries from five different McDonald's, Burger King, and Wendy's outlets in Manhattan and tested them at an independent laboratory for trans fat content.
The center reports that McDonald's fries had the least trans fat (0.2 grams per serving).
However, Wendy's had 3.7 grams per serving, and Burger King had 3.3 grams per serving.
They do clarify that Wendy's serving size was 25-percent larger than Burger King's.
"McDonald's has proven that restaurants can truly eliminate artificial trans fat," said Jacobson.
CSPI was careful to state that the new results do not necessarily mean that Burger King and Wendy's are violating New York City's new requirement.
In fact, trans fat levels were found to have halved, suggesting that the suppliers were still using trans fat to partly fry the fries prior to shipping.
Trans fats are formed when vegetable oils undergo a process of hydrogenation, which changes the molecular configuration and properties of oils used for baking, frying, shelf-life, and other purposes.
But hydrogenation creates trans fatty acids in the oil, and these have been repeatedly linked to raising blood cholesterol levels and promoting heart disease.
Trans fats first came into the public eye in 2003, when a lawsuit filed against Kraft Foods for the trans fat content of its Oreo cookies resulted in the firm reformulating its trademark product.
Since then, increased public awareness and new federal regulations requiring manufacturers to label the trans fat content of their products have resulted in a mass reformulation effort throughout the food processing industry.
But the battle surrounding trans fats has since moved into the foodservice sector.
This sector was first challenged on this issue in 2003, when McDonald's was sued for reneging on its promise to reduce the amount of trans fats in its oils.
The action resulted last year in an $8.5m settlement.
Fast food chains KFC and Taco Bell announced they would transition to trans fat free cooking oils.
Other restaurant chains to voluntarily slash trans fats include Wendy's, Ruby Tuesday, Chili's and Legal Sea Food.
According to the New York City Board of Health, heart disease is the city's leading cause of death, resulting in 23,000 deaths in 2004.