Je fais opposition sur ma carte bancaire.

Here faire opposition is a fixed French expression used especially in banking and administration. With a bank card, it means to report the card so it is blocked and can no longer be used.

So this is not about opposing something in the general English sense. It is a specific practical action: stopping the card after loss, theft, or fraud.

Because in this context French normally uses the idiomatic expression faire opposition.

A native speaker would say:

• faire opposition sur sa carte
• faire opposition à sa carte in some contexts
• mettre sa carte en opposition

But j’oppose ma carte bancaire would sound unnatural here.

This is one of those cases where French prefers a set phrase rather than the verb that looks like the obvious English equivalent.

Because faire opposition works as a fixed expression. French often has these faire + noun expressions where no article is used.

Compare:

• faire attention
• faire peur
• faire opposition

So opposition here behaves almost like part of a verbal chunk, not like a regular countable noun.

Not literally. Here sur means something like regarding, on, or for the card in a banking sense.

So sur ma carte bancaire means:

• concerning my bank card
• on my bank card account/record
• against the use of my bank card

It does not mean physically on top of my bank card.

This kind of sur is common in service or administrative language.

No. French speakers may also use other expressions, such as:

• Je fais opposition à ma carte bancaire.
• Je mets ma carte bancaire en opposition.
• Je fais bloquer ma carte bancaire.

The sentence you were given is understandable and idiomatic, especially in a banking context, but it is not the only way to express the idea.

Not exactly.

In French, carte bancaire usually means a bank card: the card linked to your bank account. In everyday use, this often covers what English speakers might call a debit card, and sometimes more generally a payment card issued by a bank.

So you should not automatically translate carte bancaire as credit card every time. It depends on the actual banking system and context.

Because carte is a feminine noun in French.

So you say:

• ma carte
• une carte
• la carte

If the noun were masculine, you would use mon instead.

Je fais is the present tense of faire.

It can mean:

• I am making
• I make
• in context, often simply I’m reporting/blocking

In practical situations like a phone call to the bank, the present tense often describes the action you are carrying out right now.

Yes, but in real life you would usually say a fuller sentence, for example:

• Je voudrais faire opposition sur ma carte bancaire.
• Je dois faire opposition sur ma carte bancaire.
• J’aimerais faire opposition sur ma carte bancaire.

These sound more natural in a conversation with customer service because they include the polite framing around the request.

No. In this context, a French speaker will understand it as the specific banking action of having the card blocked.

That is because faire opposition has a specialized meaning in administrative and financial French. So even though opposition looks like the English word opposition, the phrase as a whole has a much narrower meaning here.