I'm currently contracted and paid by Company A. Company A has clients Company B and Company C whom I am developing for.

Company A has been delinquent in paying me on time repeatedly for the past few months. Their initial response was due to billing errors, which was understandable, but their last reason was that they haven't been paid by Company B on time and are thus delaying paying me.

This has been going on for 3 months now and my patience has run out. I'm considering ceasing all development work for their clients until they pay their outstanding debts. How do I communicate this to Company B and C without tarnishing any relationships? I don't want to appear as though I am abandoning them as clients, but I also don't want to continue to get stiffed by Company A. Feel like I don't have much leverage aside from getting Companies B and C to pressure them as well. What should I do?

Unfortunately I don't have the resources for a lawyer and I'm also not a citizen in the country of any of these companies.