Record-setting bodysuits were outlawed by FINA on Friday, with swimming's governing body taking a major step to limit technology in the pool.
FINA has come under criticism for its failure to regulate the rapid advances in swimsuit technology that has led to 108 world records last year and nearly 30 so far this year.
Some suits are suspected of creating "air trapping" effects that artificially enhance speed.
A U.S. proposal to limit the amount of swimsuit coverage — between the waist and knees for males, not beyond the shoulders or below the knees for females — was overwhelmingly passed by the FINA congress, meeting in Rome during the world aquatics championships.
The new rule also says suits shall only be made from "textiles," but that term has yet to be defined.
"The most important thing is that it's textile only," Mark Schubert, head coach and general manager of the U.S. national team, told The Associated Press. "I think we sent a strong message as to our feeling of what the suit should be."
The new rules won't take effect at these swimming championships, where dozens of world records could be set in suits made from materials such as polyurethane.
The legislation was passed as a general rule, but then a subsequent motion from Britain to make the rules part of FINA's bylaws was accepted, putting the matter in the hands of FINA's bureau.
General swimming rules only come up for discussion at the FINA congress every four years, whereas the bureau meets several times each year, and can also convene on short notice.
"We didn't disagree with the U.S. proposal, but we wanted the flexibility to amend it as technology moves on, and we can now," said David Sparkes, the chief executive of British Swimming. "Technically, the bureau could even convene over email.
"For sure it's not the end of the road in terms of innovation."
But bureau bylaws pertain only to world championships and Olympics.
USA Swimming will conform to the international standard.
'There are many other things'
The question of how to define textiles is unlikely to be determined until the next FINA bureau meeting in September or October.
"This is only a small part of [the problem]. It's not only shape and material. There are many other things," FINA executive director Cornel Marculescu said.
With the high-tech bodysuits still in use, multiple records are expected in this meet — records that could stand for some time.
The Americans originally wanted men's suits to be limited only from going beyond the shoulders or knees.
Paolo Barelli, president of the Italian swimming federation, had a mixed reaction. Italy was opposed to the new suits before last year's Olympics, when the Americans and Australians benefited with Speedo's LZR.
Now, bodysuits from Italian manufacturers Jaked and Arena are considered the fastest on the market.
"All the nations now need to study this rule carefully, without regard to manufacturers or market factors," Barelli said. "We've got to take a step backward, with precise rules equal for everyone. My Anglo-Saxon friends need to realize that this mess began in January 2008."
A spokesman for Swimming Canada said Canadian swimmers have the choice to wear what suit they wish, with many wearing the Jaked suits.
Jaked suits were not included on the list of approved suits FINA released earlier this year, but they were not on the banned list, either.
Hoping to avoid any distractions caused by the issue, the British team barred media from asking its swimmers about the issue after arriving in Rome for the world championships.