Started to receive advertisement from attorneys saying that a credit card company is going to garnish my salary? I have tried to settle a monthly payment with them.

A garnishment requires that a judgement be awarded to the creditor (expect for certain govt debts).

They will have to file suit and win first.

Once they have a judgement, in most areas there is no other notice, so if they already have a judgement, yes they can.

If there is no current judgement, they will have to get that first.