Support for Propositions 30 and Proposition 37 is falling among California voters, according to a USC Dornsife/Los Angeles Times Poll released Thursday.

Only 46 percent of respondents said they were in favor of Prop. 30, Gov. Jerry Brown’s tax initiative, marking the first time support has fallen below the 50 percent margin. Prop. 37, which would require foods containing genetically modified ingredients to be labeled, dropped to garnering 44 percent support from California voters.

Prop. 30, which would raise revenue for public education and public safety by temporarily increasing the state sales tax by one-quarter cent and raising personal income taxes on citizens who earn more than $250,000 a year, has continually declined in the polls from a level of 61 percent support in March. Experts, such as Dan Schnur, the director of the USC Dornsife/Los Angeles Times Poll and the Jesse M. Unruh Institute of Politics, attributed this decrease in support to the public perception of the state government.

“Governor Brown has successfully convinced voters that more spending on the state’s public schools is a good thing,” Schnur said. “What he has yet to do is convince them that state government can be trusted to spend their tax dollars wisely.”

Additionally, Drew Lieberman of the Democratic polling firm Greenberg Quinlan Rosner, which helped conduct the poll, said that though voters want to protect education, they do not have enough trust in the measure.

“Nobody likes to cut education,” Lieberman said, “but there is a lack of trust as to how the money will be allocated.”

Schnur also said a large amount of negative advertising by proponents of Prop. 38, the direct competitor with Prop. 30, could have hurt its approval. Similarly, experts said negative messaging directed at Prop. 37 knocked it down in the polls.

“The most significant driving force behind this shift is the amount of money that the opposition has put into the campaign,” Schnur wrote on the Dornsife website. “When voters hear a message so much more strongly from one side than the other, it’s not surprising to see the poll numbers move like this.”

The USC Dornsife/Los Angeles Times Poll is conducted at regular intervals. The poll, which was conducted by Democratic polling firm Greenberg Quinlan Rosner and Republican polling firm American Viewpoint, surveyed 1,504 registered California voters.