Not necessarily. For the world trade authorities to be able to step in there needs to be actual collusion going on (and they need to be able to proof it or at least have strong indications of that happening), at least last time I checked.
Competitors not pressuring each other in some sort of "silent understanding without active collusion" is quite tricky to prevent if you have only very few competitors (see HDD market as another example besides the DRAM market). So long as all competitors are more or less satisfied with their market share and profits they have less motivation to push their competitors out of the market completely.
This doesn't happen in all markets with few competitors, of course.
Here in Switzerland we have some sort of price watch dog authority guy who can step in if prices are unreasonably high without there being an actual (illegal) cartel. He's quite busy with the telecommunications companies at the moment

.
I am not sure if something like that exists on an international level though.
In general, the fewer competitors you have, the easier it is for them to reduce price pressure on each other without there actually needing to be a cartel. And that is, to the consumers' detriment, not illegal in and of itself.
EDIT:
That's another thing of course. Something being illegal does not necessarily deter companies from doing it. The most likely punishment if you get caught is a fine. So as long as
Code:
(profits w/ price fixing)-(fines to pay)>(profits w/o price fixing)
there's still enough incentive to do illegal shenanigans for some companies.
/EDIT