I can't find a lot of info on this, but it is apparently in the Insiders area on ESPN.

Here is a quote taken from the link:

"ESPN’s Adam Schefter is reporting that the Arizona Cardinals have placed a restricted free agent tender on wide receiver Steve Breaston, according to a league source. Schefter says a few teams used this tactic last week, and he expects to see a lot more of it before the CBA expires on Friday. He says it’s a team’s best chance to restrict a player’s movement whenever free agency actually begins."