Meeting dishonest ex-supervisors at large international conference -- Should one speak out? I have returned to my country after one negative experience as a postdoc in China.
In short, I was hired based on false salary &amp; funding expectations supported by shady vague contracts written in Chinese. I stayed until the end as to escape a raging crisis at home. 

Now I am back home, among long-date colleagues &amp; collaborators. A large international conference in our field of study starts today. The very same PIs who lured me into their trap are coming, now in my country, actively seeking for new candidates. Surely they expect me to treat them politely, coldly at best. These people owe me a lot of money, plus stolen time and project ideas.

I think they expect me to stay nice and quiet for fear of getting bad recommendations and in the hopes of perhaps getting paid/compensated in the future. The culture here is certainly different from what they expect. In just few hours I will meet them at the conference hall, for the opening.

I am revolted. At least in my country, LoRs are not required for getting jobs, and I do not think they're too influential outside of their institutions. 

Should I openly expose them? Or would that just label me as some begrudged nuthead?

There is one special roundtable about work ethics included, and I am thinking of approaching the organisation about this. Any suggestions, ideas on this, would be appreciated.

P.S. This is not in the US.

UPDATE:

Finally the event is coming to an end. I have carefully considered the views of commenters and answers here. Thanks to all for so much attention.

I have avoided the scammers as best as I could. They approached me individually, on different casual occasions, to greet and initiate some chat. I was just plain cold, cutting it short. Fortunately they got the message and have been also avoiding eye contact and interaction.
I have outlined the absurd situation to a large number of peers, yet only when asked. “How was it in China”, “I remember you complaining about some problems, how did that fare” etc. I did not mention names, except when directly asked for confirmation. 
A couple of friends are part of fhe organizing comitee. They agree in that it’s best to only bring this up to the chairman in case these scammers are openly advertising positions with false information. 
I did contact some local reporters I know who asked for an outline. Yet once they had the story they didn’t reply. I don’t think then this will hit the newspapers unless something new and remarkable happens.

The event ends tomorrow. They might approach me one last time. If they do I’ll comment below. Otherwise I’m leaving this at this. I’ve focused on intensively networking and getting collaborations moving, learning new ideas. Much easier without having to interact with this mess. Hopefully I’ve warned enough people to at least avoid someone else fall in this trap. Hopefully they’ll move to a different field or just stop. Thanks to all here.
There is a lot going on here. If you want to play power politics make sure that you have the power first. 

You contemplate making an accusation. Depending on local law and custom this could open you to a charge of slander that you would have to defend. Far in the past a duel on the green would be seen as the appropriate response. Now it is lawyers instead of pistols, of course. 

If you can make the claim fairly and can also do so anonymously you protect yourself. If the journalists you intend to speak with can really protect "their sources" (i.e. your identity) it might be possible. But they will need evidence even though they are less susceptible to a charge of slander. 

But an emotional response won't help anyone and might reflect badly on yourself. 

But I see your dilemma. Others may be at risk here if you don't make some attempt. I think that the conference chairs that I have worked with would listen to your complaint if you can contact them. This won't guarantee anonymity, of course, but in the best case it could put other powerful people in your camp. On the other hand, if the committee is somehow aligned with the PIs in question it would be the worst situation of all. 

One rather scary possibility is that you confront them privately and tell them your complaints and that you don't like to see them recruiting others into the same situation you faced. If you know of any others who already faced the same situation and you can confront the PI as a group it would be even better. Some people have no shame at all and some are driven by forces even they can't control, but you might let them think that withdrawal is a better option than continuing. Scary, though. 

Ethics don't require, in a case like this, that you put yourself at risk to save others.