(CNN) - Actress Jessica Biel spent a day this week in Sacramento meeting with lawmakers and anti-vaccination advocate Robert F. Kennedy Jr. to discuss a controversial vaccine bill.
SB 276, which is currently under review, is a California state bill that seeks to limit medical exemptions from vaccinations. The bill has been opposed by anti-vaccine advocates, as it effectively makes it harder for parents in the state to find a way around the strict rules that require children to receive vaccines before being enrolled in public or private elementary and secondary schools.
Biel has one son with husband Justin Timberlake.
A representative for Biel did not immediately respond to CNN's request for clarity on Biel's views on vaccines.
"Please say thank you to the courageous @jessicabiel for a busy and productive day at the California State House," said Kennedy, chairman of the Children's Defense Fund, which opposes the bill.
In another photo, Kennedy and Biel posed with Democratic Assemblymember Autumn Burke.
Biel commented on the post: "Great meeting with both of you today."
Kennedy called Biel "a very effective advocate" in an interview with The Daily Beast.
"She was very strong and very knowledgeable," he said.
State health officials estimate that more than 40% of the 11,500 medical exemptions expected to be requested each year would be denied under the bill, according to the Los Angeles Times.
In April, the CDC confirmed the US was amid the largest measles outbreak since the disease was declared eliminated in 2000.
Most cases in the United States have emerged in communities with low rates of vaccination against the virus, according to public health officials.
CNN's Jacqueline Howard and Debra Goldschmidt contributed to this report.