The court shall impose a monetary sanction under Chapter 7 (commencing with Section 2023.010) against any party, person, or attorney who unsuccessfully makes or opposes a motion to submit tardy expert witness information, unless it finds that the one subject to the sanction acted with substantial justification or that other circumstances make the imposition of the sanction unjust.
Source:
Section 2034.730, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=CCP§ionNum=2034.730..