While it's not aggressively kept in check, tampering is known to happen in the NFL. What constitutes tampering? If someone from an organization holds a private meeting (or simple conversation) with a player that's under contract or held by exclusive negotiating rights with another team. If that organization makes it known (either privately or publicly) that their interesting in obtaining that player, that constitutes as tampering.
But that doesn't mean an ex-player with no affiliation can't clamor for a player to join his former team.
With Chuck and Vince on Fan AM 1060, former Arizona Cardinals quarterback Kurt Warner was asked how the team should address their quarterback situation.
"I think a guy like Carson Palmer would be tremendous in that kind of system."
The Bengals remain hard-headed in their position that Carson Palmer will not be traded, forcing him into self-imposed retirement. Even if the Bengals wanted to trade Palmer, they can't until there's a collective bargaining agreement resolution between the owners and players.