Many soups sold in high street cafes and supermarkets may not offer the healthy option customers are seeking, a pressure group has warned.
Consensus Action on Salt and Health (Cash) said 25% of 575 types of soup it analysed failed to meet Food Standards Agency targets on salt content.
However, it said there had been a 17% drop in the amount of salt in ready-to-eat ranges since its 2007 survey.
Experts say high salt intake raises blood pressure and the risk of strokes.
For its survey, carried out between December and February, Cash tested soups from a number of supermarkets and high street chains.
The Food Standards Agency's target for soup is that each 100g portion should contain no more than 0.6g of salt.
Its recommended maximum daily intake of salt for an adult is 6g.
Among the worst offenders highlighted by Cash was cafe chain Eat's 907g Bold Thai Green Chicken Curry soup, which Cash said contained more than 8g of salt.
Even Eat's smallest 340g-sized portion had 2.8g of salt, nearly half the daily recommendation and more than a Big Mac and fries, Cash said.
Eat, which has 98 shops nationwide, said it had reduced salt in all its soup stocks and would continue to do so, but said it needed to happen gradually for people's tastes to adjust.
Brand director Faith MacArthur said its largest sized soup was often shared and represented a tiny part of soup sales.
Cash chairman, Professor Graham MacGregor said: "The majority of the food industry is slowly taking out the salt from food, including these soups.
"We commend the progress so far, however they haven't gone far enough if we are to save the maximum number of lives."
Spokeswoman Katharine Jenner added: "People tend to think salt is only in crisps, snacks and ready meals. But this survey shows huge amounts of salt can be hidden in seemingly healthy choices such as soup.
"We urge manufacturers to reduce their salt content immediately."
Cash said among supermarket-own brands it tested, 93% met 2010 FSA salt targets, compared with 66% of branded products.
Among products on sale in supermarkets, 23 contained 2g or more salt per portion, Cash said. Of these, 18 were from brands including Heinz and New Covent Garden.
When it came to fresh supermarket soups, Cash said, the highest in salt content was New Covent Garden's Scotch Broth at 2.4g of salt a portion - six times higher than the lowest, Tideford Organics Moroccan vegetable at 0.44g.
Prof MacGregor urged consumers to boycott products high in salt.
The New Covent Garden Food Company said it had consistently reduced salt levels across its range over recent years and had beaten the Food Standards Agency's average target for soup.
"We also feature the government-approved FSA traffic light labelling system, which clearly shows all our soups fall within either green or amber classifications for salt," a spokesman said.
Heinz said its entire soup range was already within average targets and its work to cut salt further continued in line with consumer taste.