Bynes, 27, was arrested Thursday night after she allegedly tossed the item while police were in her apartment investigating a complaint that she was smoking marijuana in the building lobby. She was charged with felony count of tampering with evidence, as well as reckless endangerment and marijuana possession.
She took to Twitter Saturday, claiming one of the officers sexually assaulted her, the New York Post reported.
"He slapped my vagina. Sexual harassment. Big deal," she posted.
She said the police report of what took place in her apartment was a lie, CNN reported.
"[The officer] lied and said I threw a bong out the window when I opened the window for fresh air. Hilarious," she tweeted.
New York Police Department spokesman Detective Brian Sessa told ABC News the department is conducting an investigation into Bynes' allegations.
A second police source, whose name was not reported, said Bynes' allegations of sexual assault are false.
"She was on the phone with 911 making the allegations before officers entered the apartment," the source told ABC News. "An independent witness, the building manager was [there too]."