According to their documentation on Package Intercept dated May 2015 the Intercept service is available for "All domestic mail classes except Standard Mail and Periodicals" that have a tracking number. So I don't know why they'd say it is for only priority. On the site they ask for the tracking up front to begin the Intercept request process. It goes through fine until the payment screen. If there was a true issue with the tracking number it would seem they'd give you an error when the number is first entered not all the way at the last step before payment. Something is very wrong.
According to their documentation on Package Intercept dated May 2015 the Intercept service is available for "All domestic mail classes except Standard Mail and Periodicals" that have a tracking number. So I don't know why they'd say it is for only priority. On the site they ask for the tracking up front to begin the Intercept request process. It goes through fine until the payment screen. If there was a true issue with the tracking number it would seem they'd give you an error when the number is first entered not all the way at the last step before payment. Something is very wrong.