Well, by the ACLU. They describe what they mean in the fact sheet linked from the page that was provided:
The border, however, has always been an exception. There, the longstanding view is that the normal rules do not apply. For example the authorities do not need a warrant or probable cause to conduct a “routine search.”
But what is “the border”? According to the government, it is a 100-mile wide strip that wraps around the “external boundary” of the <?XML:NAMESPACE PREFIX = ST1 />United States.
(I left the XML error in there just for the lulz.)
You can disagree with their analysis, but it's pretty clear that their position is that normal 4th amendment rules are being superseded merely because of a rather wide proximity to the border.
The border, however, has always been an exception. There, the longstanding view is that the normal rules do not apply. For example the authorities do not need a warrant or probable cause to conduct a “routine search.” But what is “the border”? According to the government, it is a 100-mile wide strip that wraps around the “external boundary” of the <?XML:NAMESPACE PREFIX = ST1 />United States.
(I left the XML error in there just for the lulz.)
You can disagree with their analysis, but it's pretty clear that their position is that normal 4th amendment rules are being superseded merely because of a rather wide proximity to the border.