"Junk" or unsolicited calls from fax numbers aren't just an annoyance; they can be illegal, according to the Federal Trade Commission. While you can register a fax number through the "Do Not Call" registry, the Federal Trade Commission cautions that unsolicited fax numbers frequently operate outside the law and may not comply with the registry. If an unwanted fax number keeps calling your company's phones, there are measures you can take to reduce the frequency of or to block the number.

Step 1

Access the Junk Fax mode through the "Setup" mode on your fax machine. By default, most fax machines are set to Junk Fax Mode. However, it is necessary to add numbers to the "Junk" fax list.

Step 2

Select "Junk Fax" mode if it's not selected. This feature blocks phone numbers entered onto the "Junk" fax list. You must have a caller ID service to use this feature.

Step 3

Add numbers to the "Junk" fax list. According to HP.com, there are two ways to enter fax numbers onto the "Junk" fax list. You can scroll through caller ID history and select any unwanted fax numbers or enter the number manually.

Step 4

Purchase a call-blocking service. The "Junk" fax list is effective but not foolproof. Sometimes, a solicitor's fax number is unavailable. Many providers offer a call-blocking service for a fee. In addition, many business-supply stores sell call-blocking devices. When attached to your telephone, the device hangs up on calls with long-distance trunks (i.e. numbers such as 800 and 866).