Ivy Got You Covered
Sources
These websites describe the specific legislation of the states and the reasoning behind outlawing the plant:
Legislation for the Ivy
English Ivy has been outlawed in three states. Washington state and Oregon have both made the selling and growing of English Ivy as well as many other similar species of weeds illegal. Both states have categorized different species of plants and why they are illegal. The concern is the dangers to humans, other plant species and the environment. Virginia has a serious issue with the species covering entire areas of land causing other plants to die. Virginia's governor however vetoed the bill to outlaw the plant due to concern that it would cause more and more species to be outlawed, but the state house overruled the veto. This means that three states so far have noticed the serious environmental impacts that English Ivy has and have made a change to lessen the impact. More needs to be done.

Image from Conserving Carolina