Hillary Clinton's campaign has begun airing on an ad focused on the wage gap in Iowa, according to The New York Times.

The report said the 30-second ad, which wasn't publicly announced, is airing in Des Moines in Iowa City. The Iowa caucuses are just over a month away on Feb. 1.

"On average, it takes 300 Americans working for a solid year to make as much money as one top CEO. It's called the wage gap and the Republicans will make it worse by lowering taxes for those at the top and letting corporations write their own rules," the narrator in the ad says.

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The ad goes on to say the Democratic presidential candidate will work to close the wage gap, pursue equal pay for women, a higher minimum wage and lower taxes for the middle class.

On Tuesday, the campaign also began airing a radio ad in the early voting state of South Carolina in which Clinton highlights a plan to raise incomes for African American families in the state.

The wage gap theme has often been a focus of Clinton's campaign as well as for her rival Sen. Bernie Sanders, I-Vermont.

Clinton will head to New Hampshire this weekend and will be joined by former President Clinton at several campaign events.