Actually guys, neither is correct.
GM Cars have 4 pricing tiers if you read their documentation.
MSRP - which we all know
Cost - which is what the dealer pays
Employee - a discounted price, set by GM, for employees and family of employees
Supplier - a discounted price set by GM for employees of compaines that supply GM with parts or supplies.
The 4 prices are on the invoice when we get them from GM. And the dealer is correct that supplier price is non negotiable. The dealer is reimbursed a portion of that discount from GM. You are allowed to deduct any applicable rebates or incentives, or take the GMS financing rate if you qualify. You must have your company's supplier ID in order to get this price, so make sure you ahve all the info you need.
The GMS price is the second lowest available on a GM product, with the employee price at rock bottom.