A decade ago one of my writer friends demanded that I not use impact as a verb. "It is a noun and only a noun." I agreed with the first part of his sentence that it is a noun and means to have a strong and often bad effect on something or someone.
I disagree with the second part because impact can function as a verb. In researching the word, I learned that the verbal usage has been around since the early 1600s. It means to influence or to strike forcefully. For example: The down economy impacted his sales commission.
Others will allow impact only as an intransitive verb (that is, a noun doesn't follow the verb or take a direct object). That seems arbitrary to me. To make the verb intransitive, they add the preposition on. The new law impacted on the poorest people. I see nothing wrong with writing it this way: The new law impacted the poorest people. It had a powerful, direct influence.
I am careful and certain about the words I use.