How many Sam's Club membership vouchers can I purchase?

There is a limit of one membership voucher per person.

If you are attempting to add a Sam's Club membership voucher to your cart and encounter an error message stating that adding the item to your cart exceeds the maximum quantity allowed, you may need to refresh your page, and check to see if you already have a membership in your shopping cart. You can view your shopping cart in the upper right corner of the page in your account. Click on the cart symbol to view any items that are waiting to be purchased.