The warning lends support to claims by Procter & Gamble, Unilever's arch-rival in the detergents market, that the new powder - called Persil here and Omo on the Continent - harms clothes. And it comes only days after the two companies settled a legal dispute over P&G's claims.
Consumentenbond said tests carried out by an independent research institute on its behalf had shown clothes washed in Omo Power caused more wear and tear than rival products.
Andrew Seth, managing director of Lever Brothers - the Unilever arm responsible for Persil - said there had been 3 million washes in the product before its launch and 40 million since, with no problem. He said he would examine the conditions of the Dutch tests, and accused P&G of resorting to 'desperate tactics' to sabotage the launch.
Over the weekend, P&G issued photographs of boxer shorts, trousers and other garments washed in Persil Power, which showed substantial wear and tear compared to those washed in its own Ariel Ultra. Mr Seth said these were in abnormal conditions, in its own laboratories, and did not reflect the performance in consumers' own washing machines. But he added that the formulation had been changed slightly so that the damage would not occur even in the laboratory. Consumentenbond says it will test the new formulation.
Unilever has agreed to buy two state-owned margarine factories from Kazakhstan for dollars 60m ( pounds 40m).