Is it possible to have customers to sign a "blanket" authorization for a company to bill their credit card?

The situation is that customers run up relatively small bills that vary from month to month (less than $100 but it is seldom the exact same sum every month) and to avoid having to deal with collecting from slow payers (and deadbeats), I was thinking about have customers just give a blanket authorization. Any suggestions you might have (and also suggested wording for the authorization) would be appreciated. Thanks!