CMS is alerting providers that certain individuals are sending faxes to physician offices posing as the Medicare carrier or Medicare Administrative Contractor.  The fax instructs physician staff to respond to a questionnaire to provide account information within 48 hours in order to prevent a gap in Medicare payments.  CMS recommends that providers check with their contractor before submitting any information in response to such a solicitation, and to only send information to actual contractor addresses posted on the CMS web site.