From the Associated Press:

Attorney General Eric Holder says the federal government will enforce its marijuana laws in California even if the state's voters approve a ballot measure to legalize the drug. […]

He made the comments in a letter to former chiefs of the U.S. Drug Enforcement Administration. The Associated Press obtained a copy of the letter, dated Wednesday.

"We will vigorously enforce the CSA against those individuals and organizations that possess, manufacture or distribute marijuana for recreational use, even if such activities are permitted under state law," Holder wrote.

He also said that legalizing recreational marijuana in California would be a "significant impediment" to the government's joint efforts with state and local law enforcement to target drug traffickers, who often distribute marijuana alongside cocaine and other drugs. Holder said approval of the ballot measure would "significantly undermine" efforts to keep California communities safe.