Rather than use a postage stamp to carry out official business and representational duties (such as corresponding with constituents), Members of Congress are permitted to sign each envelope in the upper right hand corner. The Post Office accepts this signature, known as a "frank," in place of a stamp.

It is legally acceptable for the signature to be printed on the envelope, as opposed to personally signed. Members of the House receive almost 200 letters a day from their constituents, while the Senate average is well over 500 pieces of mail a day. Assuming each one gets answered (and thanks to computerized mail, most do), it would be virtually impossible for a Member of Congress to personally sign each letter and each envelope.

Members are not permitted to use franked mail for personal, political, or campaign correspondence. The use of the frank is paid for out of money Congress appropriates annually for running the institution. In 1996, the official mail costs for the two chambers combined was about $32 million. In 1995, it was just over $30 million. Congress pays this amount to the U.S. Post Office, which treats it as postal revenue.

The practice of permitting Members of Congress to use a frank dates back to 1775, when the First Continental Congress passed a law authorizing its use. With the exception of one year (1873), it has been in place ever since. And it has been controversial ever since. Proponents argue that few Members could afford to communicate with all the constituents who contact them if the cost had to be born personally, and that franking promotes democratic dialogue and representative government. Opponents point to episodes of abuse over the years, and cite increases in the use of the frank during election years, calling that an unfair electoral advantage available only to incumbents. Congress has responded to franking critics by reigning in the use of the frank over the years. Currently, House Members may not send out franked "mass" mailings 90 days before an election, while Senate rules prohibit Senators from doing so 60 days before elections.

The amount each Senator and House Member spends on franked mail is now fully disclosed, with annual disclosure reports issued by the Post Office, analyzing the total costs for the entire Congress. Numerous other restrictions apply and the practice of franking continues to be closely scrutinized by critics in the public and press. Any known or suspected abuses of the franking privilege by Members or their staff are reported to the attention of either the Senate Select Committee on Ethics or the House Commission on Congressional Mailing Standards for investigation.

Critics, led by Common Cause, brought a lawsuit challenging the legality of franking in the 1980's. A Federal District Court ruled that the congressional practice was appropriate and adequately monitored. The Supreme Court refused to hear an appeal, which the left the present practice in place.