Brazil's World and Olympic freestyle champion Cesar Cielo was among the quartet who tested positive for the banned diuretic furosemide after the South American country's national championships in May.
The 24-year-old Cielo, Nicholas Santos, Henrique Barbosa and Vinicius Waked, all escaped censure from their national body, but FINA appealed that decision to the Switzerland-based Court of Arbitration for Sport (CAS).
CAS are to hear the appeal on July 20 at a special meeting in Shanghai, with its final decision due no later than July 22, just two days before the marquee pool competition begins.
Cielo, who won gold in the 50 and 100 metres freestyle at the 2009 Rome World championships and is the Olympic 50 metres freestyle champion, said the positive test had been caused by a supplement he took regularly that had become contaminated.
FINA executive director Cornel Marculescu, however, said while he did not want to comment directly on Cielo's case, it did highlight the fact that swimmers needed to be vigilant on what they were taking.
"When you take a supplement you must be sure that you have done everything that the supplement does not contain any contamination by any kind of thing," Marculescu said. “You don't have to take supplements. In modern sports it is possible (to perform without them)."
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