is a much shorter way of saying "cabinet chargé du recouvrement contentieux des créances".
Such an agency will start politely by writing nice letters to the debtor asking them to pay, and ultimately, if need be, chase the debt all the way through the courts. All this is done on behalf of the creditor, for a fee, of course!

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Note added at 19 mins (2005-03-03 13:44:00 GMT)
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This answer is based on 7 years working for a credit insurance multinational. Each national company, in addition to credit insurance itself, had an arm that dealt with debt collection - having paid out the indemnity to the policy holder, the insurer would then endeavour to collect the debt (it\'s more complex than that, but that\'s the basic idea). The French and Belgians called this process \"contentieux\", we called it \"Claims and Collections\".
Disputed debts were called \"litiges\". Sometimes the \"collection\" aspect is outsourced to what is universally known as a \"debt collection agency\" (in the UK anyway)

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Note added at 26 mins (2005-03-03 13:50:40 GMT)
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In the light of your note - while debt collection agency will often mean an agency (firm) that specialises in debt collection and nothing else, the term actually refers to the legal concept of agency, i.e. acting on behalf of someone else, here the creditor, and so debt collection agency activity can be and is carried out by firms that do other stuff as well, such as accountants, general law practices, etc.

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Note added at 10 hrs 52 mins (2005-03-04 00:16:51 GMT)
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To reconcile my answer with Jane\'s:
My issue with Jane\'s answer was her use of \"disputed debt\". Not for the first time, I find Jane I probably agree fundamentally. In a collections situation, there are two elements to take into account:
a) the debt. Is the amount in dispute? The debtor may be refusing to pay because of a dispute over the amount (the interpretation I put on Jane\'s suggestion), or for some other reason (excessively late delivery rendering the goods useless, for example). Your simple French \"creance\" makes no distinction as far as this is concerned.
b) the collection procedure. This may be amicable (\"a l\'amiable\" in French as per Jane\'s reference), not involving the courts or, if the debtor still refuses to pay, it will move to litigious collection, involving the courts. This is where your French DOES make a distinction - this is the \"contentieux\" element. Most creditors will try to deal with the amicable resolution of the problem themselves, then pass the problem to a debt collection agency. The agency will also initially try the amicable route, but not for long (they just hope the debtor will realise that it\'s now become serious and pay up anyway), and they will soon move to the courts stage. Hence, while my answer does not strictly explicitly state the \"contentieux\" aspect of the collection, it is implicit in the use of \"debt collection agency\" itself. And you were, after all, looking for a short, standard way to express the French :-)