While the ABC test of employee v. independent contractor status applies retroactively, Prop. 22’s classification of some gig workers as independent contractors applies only prospectively. So GrubHub drivers, if employees under the ABC test adopted in Dynamex Operations West, Inc. v. Superior Court (2018) 4 Cal.5th 903, are entitled to back wages for the period before Prop. 22’s adoption. The decision remands the case to the district court to determine whether the drivers were employees under the ABC test and whether the ABC test applies to expense reimbursement claims under Lab. Code 2802.