'_.-Layer _off Layer1,Layer2,Layer3,LayerA,LayerB,LayerC,LayerTom,LayerDick,LayerHarry ;

The apostrophe at the beginning, and the lack of the ^C^C that you so often see used at the beginning of command macros to cancel any command that you may be in at the time, allows you to do it even within another command.  The underscore lets it work in other-than-English versions of AutoCAD.  The period forces it to use the native Layer command in case there's been any redefinition.  The hyphen suppresses the dialog box [you need that, but the preceding punctuation you can omit depending on your circumstances].  The colon at the end is an Enter to complete the Layer command -- other options could be added before that [turning some other Layer(s) on, setting a particular Layer current, etc.].