An attorney for a group of food truck and push cart vendors has written members of the Birmingham City Council to say the vendors have “serious concerns” about a proposed mobile food ordinance that they say is “extraordinarily restrictive” and, if passed as written, could drive them out of downtown. “Our organization isn’t opposed to regulation, but the complexity of this ordinance is kind of astounding to me,” David Donaldson, the attorney representing the mobile vendors, said today.