Hello and welcome Luis,
I have read other posts asking about the same thing as you are regarding providing their supplier with their credit card details as a requirement to starting business with the said supplier. And I know that this process/requirement seems so bogus and I completely understand the hesitation on your part, I would feel the same way too!
I have once asked one of the concerned suppliers, and they confirm that this process is mainly set as a back-up in case the customer fails to pay for their orders. This is also way for them to verify their customer's credibility. But please note that this is a case to case basis as each supplier has a different policy.
It might be best that you ask your supplier their reasons for asking for your credit card details so they can explain to you the reason and the entire process thoroughly.
If you need help in contacting them you can PM me their details and I can help you contact them :)