Intercantonal scope of an expense policy

A taxpayer residing in canton of Vaud receives from his Geneva based employer a lump-sum allowance for the use of his private vehicle for business purposes according to an expense policy approved by the Geneva tax authorities. The tax administration of the canton of Vaud (ACI), which does not consider itself bound by the Geneva approval, wants to verify the actual expenses. In a decision intended for publication (decision 2C_804/2021 of October 14, 2022), the Federal Court has just ruled against the ACI: when lump sum expenses have been approved by the tax authority, “the question of the adequacy between the lump sum expenses received and the expenses actually incurred by the employee does not arise, as this has been settled in advance between the employer for all of his employees, on the one hand and the tax authority on the other hand”. Most interestingly, this “also applies if the taxing authority is not the one that has accepted the employer’s expense policy. The approval by the tax authority of the canton where the employer is based is in principle recognized by all the cantons and is binding on them; this is a case of application of the principle of good faith”, the Federal Court states. The fact that a tax authority can be bound by an agreement given by an authority of another canton is not self-evident: could this ruling be extended, for example, to employees stock ownership plans, when the tax authority of the canton where the employer is based has validated the tax consequences of this plan?