Well the difficult thing here is that there is no singular law which dicates how an employee is to be compensated under these circumstances. It is a collection of laws and judicial opinions which, when read together, would support your position.
If I were to summarize it for inclusion in a letter to my employer, I'd start by referencing 29 USC § 203 & 206 (part of the Fair Labor Standards Act
), which colelctively require employers to compensate employees for all hours of employ at a rate no less than minimum wage
, and defining "employ" as all time "suffer[ed] or permit[ed] to work."
I would then cite Rutti v. Lojack Corp., Inc., 596 F. 3d 1046 (2010) for the general proposition articulated therein, that: "[w]hile the Portal-to-Portal Act clearly excludes normal home to work travel from the scope of the FLSA
,... Congress ... still intend[ed] for an employee's activities to fall within the protection of the [FLSA] if they are an integral part of and are essential to the principal activities of the employees
I would then argue that picking up parts at a remote worksite is an integral part of and essential to the principle activities of my employment, and I'd reference Dooley v. Liberty Mut. Ins. Co., 307 F. Supp. 2d 234 in support of this factual finding.
Again, please feel free to let me know if I can provide further assistance. If I have answered your question, I would be very grateful for a positive rating of my service so that I may receive credit for assisting you.