I was looking at my Representative's website to see if she had any recent press releases, and noticed the contact information. It says that postal mail is the slowest way to reach her, because all physical letters are scanned for security purposes, which adds two weeks to the process.

I'm fairly sure that's for all members of Congress, since the 2001 anthrax attacks, so for urgent issues there's the phone, email, and maybe Twitter or other social media.