Not surprisingly, it's done "on a case by case basis and so far the bloggers who have covered an argument have been able to demonstrate a legitimate press interest and have been given credentials by the lower court that heard the case before it came to the U.S. Supreme Court." She offered this summary of the credentialling procedure:
The Supreme Court's Public Information Office issues credentials to press in order for them to attend oral arguments. The Court recognizes press who have current White House or Congressional press credentials. Press interested in attending oral argument who do not have White House or Congressional press credentials are asked to have a letter (on the media organization's letterhead) sent via fax from the editor, producer, or appropriate person who has assigned the reporter to cover the case. The Public Information Officer reviews these media requests and, if approved, issues a one-day press credential on the day of oral argument. On a few occasions bloggers have requested and been granted a seat in the press section to cover an oral argument. These requests are reviewed on a case by case basis. Factors that are considered include: a blogger's ability to demonstrate a legitimate press interest in a case and documentation that the blogger was issued press credentials in the lower courts while covering a particular case. Bloggers who do not meet the criteria to be seated in the press section are still able to attend oral argument by waiting in the public line for Courtroom seats.