I would think this would be illegal. Have you called city hall?
I do know for a fact that chemical companies can not legally spray pesticides outside when the wind is over 5 mph. Contact the Dallas Regional Office at 214-631-0265 to file a complaint. Ask to speak with Mark Evans the Cheif Inspector of Pesticides.
You may want to copy the information from the following link at give it to your neighbors. If you have built a good relationship with them, they will be more apt to listen.