On Tuesday, Kennedy Jr., 65, shared a slideshow of photos of himself and Biel, 37, posing alongside activists and legislators.
“Please say thank you to the courageous @jessicabiel for a busy and productive day at the California State House,” Kennedy Jr. wrote of the actress, who is married to singer Justin Timberlake, 38. The couple share 4-year-old son Silas Randall.
Biel and Kennedy Jr. joined forces to take a stand against SB 276, a California state bill that would limit medical exemptions from vaccinations without approval from a state public health officer.
The bill would require the State Department of Public Health to develop a statewide standardized medical exemption request form made available for use by licensed physicians and surgeons.
The bill would require “the State Public Health Officer or the public health’s officer’s designee to approve or deny a medical exemption request, upon determining that the request provides sufficient medical evidence that the immunization is contraindicated or that a specific precaution regarding a particular immunization exists, based on guidelines of the federal Centers for Disease Control and Prevention (CDC),” the bill states.
When asked to describe Biel’s involvement, Kennedy Jr. explained to The Daily Beast the actress is “for safe vaccines and for medical freedom.”
He revealed to the outlet that his and Biel’s issue with the bill “is that a doctor who has made a determination — if he has found children in this state whose doctors have determined that they’re too fragile vaccinations — this bill would overrule the doctors and force them to be vaccinated anyways.”
“She was a very effective advocate,” Kennedy Jr. said of Biel to The Daily Beast.
“She was very strong and very knowledgable. Extremely well-informed. An extremely effective advocate. She knows what she’s talking about… She’s upset about this issue because of its particular cruelty,” Kennedy Jr. told the outlet.
“She has friends who have been vaccine-injured who would be forced to leave the state.”
In 2015, a source told InTouch Weekly that Biel “feels that vaccination could cause complications.” However, she has never publicly stated her position on vaccinating children against diseases.
A representative for Biel did not respond to PEOPLE’s request for comment.
California State Assemblyman Devon Mathis has also praised Biel for lobbying against the bill writing on Facebook, “It was great seeing Jessica Biel this afternoon in the Capitol. It’s awesome to have amazing partners and advocates for parental rights like her! Keep the fight alive. #VoteNoOnSB276 #CaDeservesBetter.”
Kennedy Jr. has been a controversial figure in the anti-vaxxer movement after making claims that vaccines can cause autism, ADHD, ADD and speech delay, The Daily Beast reported in February.
There is no scientific link between vaccines and autism, according to the Centers for Disease Control.