You may have a legal action against both companies if they were acting as joint buyers (both issued the PO). Regarding the Mexican company, you will be able to sue in Mexico becasue I assume this is where its domicile is located. You will also be able to sue the Singapore company in Mexico as a co-defendant, but you would have to further consider if a judgment from a Mexican court could be executed in Singapore. Either way, it is recommended to sue in such jurisdiction where you know that the buyer company has assets. If the Mexican company is broke, or just holds assets as subsidiary for the Singapore principal, go to Singapore. But if you think that the Mexican company might have enough assets to entertain your claim, then definitely sue in Mexico. The USA and Mexico have several treaties that make it much easier than suing in Singapore. If you want more information about the process of collection and litigation in Mexico go to our website at www.hmhlegal.com