No, you are incorrect. Your merchant account can be suspended for that, according to the merchant agreement that you sign to be able to accept cards. This is not my opinion, this is clearly spelled out in the contract. The link above is the one for Mastercard, and it clearly counts as a 'merchant violation.' You can offer a discount for other forms of payment- you may not mark up for CC sales.
Again, I am not concerned about the price of things, heck, I have over $3000 into just my AR- I just feel that if you sign a contract with someone, you should stick to it. I am a contractor, so I have spent many an hour and many a dollar meeting the terms of my contracts, as written- why shouldn't others?