A gift card gifted by your boss is considered taxable income. Even a small gift card that allows you to buy whatever you like is income that you have to pay taxes on. A gift card is tax free only if it has been given for the purchase of a specific product or service. According to the taxation authorities, cash or bonuses such as unspecified gift cards given on Christmas are considered as income and they are taxed the same way that your regular income is taxed.
Tax free Christmas gifts include gift hampers, Christmas ham, cognac, wine or other items, which cost 100 euros at most. However, the prerequisite is that all workers in the company receive the same gift.