A woman named Rebecca Lee Dalelio was arrested Friday afternoon inside the chambers of the California State Capitol building after cops say she threw something from what they described as a "feminine hygiene device containing what appeared to be blood."

She chucked the red, blood-like liquid down below from the upstairs balcony area ... where she and other anti-vaxxers were watching in silent protest as state senators wrapped up the last day of the legislative year with a vote on some last-minute measures.

The liquid -- which eyewitnesses say came from a menstrual cup -- splashed a few state senators, including Sen. Melissa Hurtado, as well as some documents and desks.

A video captured a woman screaming, "That's for the dead babies." The Senate session went into recess and concluded in private chambers shortly afterward. The video also shows a woman -- who's presumed to be Dalelio -- being escorted out into the hall by officers, where she continues her rant on dead babies, saying ... "Their blood is on your hands."

The incident starts around the 43:10 mark of the video, when the alleged blood-throwing took place.

The protest follows two California bills that were signed into law Monday by Governor Gavin Newsom, which will go into effect on Jan. 1, 2020 ... and are meant to tighten regulations around doctors who write notes to exempt certain kids from vaccines at school.

If the doctors issue more than 5 exemptions in a year, public health officials can review the passes. Schools that fall below a certain level of vaccination rate are also subject to scrutiny.