From Guns.com:

An Assembly bill now in the Senate would regulate “firearm precursor parts” sold in California through licensing, reporting and background checks.

The measure, AB 2383, passed the Democrat-controlled Assembly last month 45-29 and is currently working its way through the Senate. The proposal would mandate background checks on many of the components needed to build or repair firearms and regulate those who sell them through a licensing scheme. Supporters argue it will save lives.