LANSING, Mich — If you turn on the television this week, you're likely going to be seeing the beginning of months of political advertisements.

The conservative group Americans for Prosperity is spending nearly $1.7 million on a TV ad criticizing Democratic gubernatorial candidate Gretchen Whitmer, saying she backed policies of former Gov. Jennifer Granholm and voted for tax increases as a legislator.

The 30-second started Thursday and will run for three weeks. Americans for Prosperity is backed by the billionaire Koch brothers.

The ad points to Whitmer's 2007 votes to raise taxes to address a budget deficit. It's being released the same week a pro-Whitmer group launched an ad introducing her to voters before August's primary.

Whitmer spokesman Zack Pohl said the Koch brothers are attacking Whitmer because they know she is the strongest candidate to beat Republican candidate Bill Schuette in November. Pohl told us the ad is misleading in several ways and says Whitmer repeatedly took on former Gov. Granholm in Lansing.

The attack ads come as Whitmer launches her first set of television advertisements that cost nearly $2 million.

In the 30-second ad that starts airing Tuesday, Whitmer says she "fought for working families" in the state Senate, where she helped to raise the minimum wage and expand Medicaid health insurance to more than 600,000 residents. She says there is more to be done, though, such as spending to boost workers' skills and repealing the "retirement tax."

The pro-Whitmer ad and an additional one to be aired later are being paid for by Build a Better Michigan, a nonprofit organized by Whitmer allies. Her campaign plans to air traditional ads soon.

Democratic challenger Shri Thanedar also is starting a second round of advertisements. He has spent almost $6 million of his own money for his campaign and according to the Michigan Campaign Finance Network he's spent nearly $2 million on broadcast television ads.