Companies that add a surcharge to credit card purchases

I heard from somewhere that the DTI does not allow companies to add a surcharge for credit card purchases... If that is true, these companies are in violation. These companies might claim: "Everybody's doing it!" Duh! When is that ever a justifiable justification?

Villman Computer Systems, Inc. (specifically, Katipunan Ave., Quezon City branch; 5 or 6% surcharge yata)
SOS (Save on Surplus) SM Centerpoint Branch (5 or 6% surcharge yata)
PC Express (specifically, Katipunan Ave., Quezon City branch; 5 or 6% surcharge yata)
Monakiki SM Centerpoint Branch (5% surcharge)
PhilScan Travel (a travel agency; they're offer one of the cheapest rates and if only for that, I'm still okay with them but... still, they are in violation! 3% surcharge lang naman)

If I'm mistaken, please correct me!