Republican U.S. Senator Pat Roberts has signed a pledge sponsored by a conservative women’s organization to repeal, defund and dismantle the Affordable Care Act, also known as Obamacare.

The pledge is sponsored by Independent Women’s Voice, which considers the pledge a “litmus test” for candidates that it either supports or opposes.

“Signers of the Repeal Pledge believe that this law cannot be ‘fixed’ and that stopping its implementation and ultimately repealing it are necessary first steps to ensure that citizens and their doctors, not government bureaucrats, have choice and control over their health care, and that medical care in our country becomes more affordable and available,” the organization said in a news release announcing Roberts’ signing.

Roberts is seeking his fourth term in the U.S. Senate. He faces a primary challenge from Tea Party-backed candidate Milton Wolf, a Johnson County radiologist who signed the repeal pledge earlier.

Independent Women’s Voice describes itself as a “nonpartisan, nonprofit organization for mainstream women, men and families.” It was formed in 1992 and grew out of an ad hoc committee that supported the nomination of Clarence Thomas to the U.S. Supreme Court after he was accused of sexual harassment.

According to the website OpenSecrets.org, which tracks independent campaign expenditures, the organization has spent nearly $370,000 so far this election cycle, primarily for ads opposing Republicans and Democrats who do not support its positions.