Ryan Sandler and Charles J. Romeo, both of the CFPB have written The Effect of Debt Collection Laws on Access to Credit. Here's the abstract:
Debt collection by third party collection agencies is an important part of the market for consumer credit, but has been little studied in the economics literature. Regulations on debt collection practices can protect consumers, but may also lead to unintended consequences as the costs of better practices are passed on to creditors, who in turn restrict consumers' access to credit or raise prices. Using detailed administrative data on new credit card accounts, this paper studies the effects of four recent state laws and regulations that placed restrictions on the conduct of debt collectors. We find that such restrictions reduce access to credit card accounts and raise prices for credit cards, but that this effect is very small of a similar magnitude to a minor change in the average consumers' credit score.
UPDATE: An earlier version of this post indicated that Mr. Romeo was at both DOJ and the CFPB but apparently that is not correct and he is at only the CFPB.