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DENVER (KDVR) — More than 300 people signed up to testify in opposition to SB 163 Wednesday, which impacts parents in Colorado who do not vaccinate their children.

The legislation affects parents who don’t vaccinate over personal or religious beliefs.

According to the bill, parents would need to visit a physician to sign an exemption form or watch an online video sanctioned by the state.

“Both of these approaches have been used in other states to increase vaccination rates,” Dr. Sean O’Leary, an infectious disease expert testified.

The majority of testimony, however, came from parents in opposition to the bill. Many of them read harassing comments they have received from the public over their parental decision.

Testimony is expected to last late into the night on Wednesday.