JEFFERSON CITY, Mo. — Americans for Prosperity is launching a $1.2 million television ad buy encouraging Democratic Missouri Sen. Claire McCaskill to support a tax overhaul.

The group backed by billionaire brothers Charles and David Koch on Thursday announced the ads will run for three weeks starting Friday.

In the ad, a woman praises a tax overhaul as bringing more money to “everyday Americans.” Then a narrator says McCaskill is standing in the way, although the tax plan is still evolving in Congress.

The ad encourages viewers to call McCaskill to tell her to the support the tax overhaul.

McCaskill on Thursday called the ad deceptive. She said she would support helping lower- and- middle-class Missourians but oppose a bill to help the wealthy and bankers. She says she has to see the plan.