The following is a letter I just sent to the manufacturer of the tear gas used by the Egyptian and other Arab governments. You can contact them yourself here. Feel free to borrow any or all of the letter below, if you like.
To the management of Combined Systems, Inc.,
I am writing to ask you to end your relationship with the Egyptian government and other authoritarian governments who have misused your products to kill their own citizens.
To be clear, I do not believe you have acted criminally. To the best of my knowledge, your company has followed every single regulation regarding the sale of military hardware to foreign agents. As of yet, the US government has not applied the Leahy Law to the Egyptian security forces for the violence it has committed against its civilians. Therefore, you have every legal right to sell your products to the Egyptian government.
Nor do I believe you have acted repugnantly. When used properly, your products have the potential to save lives by allowing security forces to respond non-lethally to security disturbances. You are not pigs for selling your products to American allies – though some have called you just that. After all, it is ultimately the responsibility of the Egyptian government to use your products humanely.