Courage Campaign posted an online video, claiming Kardashian made $12 million last year.
However, the group says she only paid 1 percentage point more in taxes than someone who made $47,000 a year.
The video is part of the group's campaign for a proposed November ballot initiative to raise taxes on the wealthiest Californians. The video ad, which is posted at www.Taxkimk.com, urges Kardashian to support the proposal for a tax increase.
There's been no comment from Kardashian so far.
The Courage Campaign and the California Federation of Teachers are among the groups backing a so-called millionaire's tax that would raise income tax rates by 3 percent to 5 percent for individuals who make more than $1 million a year.
Proponents say the tax would raise about $6 billion to help fund public schools and local services that have been hit hard during the recession, such as social services, programs for the elderly and public safety.
The Associated Press contributed to this report.