Here's the link, and the text of the letter:
"On May 20, the Washington State Association of Letter Carriers passed a resolution calling for Congress to oppose warrantless searches of U.S. mail in postal custody.
This resolution was in response to the president attaching a signing statement to a postal reform bill in which he declared that first-class mail could be opened in “exigent circumstances.”
Constitutional scholars have looked at this issue and determined that no such wiggle room exists for the president. Therefore, his adding this phrase to the law is not constitutional and could lead to federal agents or their subordinates engaging in this practice.
Letter carriers have historically been viewed as the most trustworthy public officials in the federal government, because we make sure people get their mail without anyone else reading it or otherwise violating their privacy.
We all want terrorists to be stopped from attacking Americans, but doing it without a court order is unnecessary. It’s really quite easy to get a warrant to look through a terrorist’s mail. It’s much harder to get a warrant to search someone who isn’t a threat to the United States.
As letter carriers, we believe that it should remain difficult to search someone who hasn’t done anything wrong.
Isn’t it about time the president heard from his own employees about what the Constitution is all about? If his own close aides don’t have the courage to explain it to him, we letter carriers are happy to oblige."