Teams can interview any assistant coaches from other teams who are not in the playoffs. They must, however, request permission if a coach is under contract with another team. Teams are also allowed to interview assistant coaches who have a first-round bye in the playoffs. However, the interview must take place that week. Candidates can choose to decline the interview to focus on preparing their current team for the postseason.

If an assistant coach’s team loses in the Wild Card round, the candidate can interview with any team that goes through the proper channels to secure an interview. However, if the assistant coach’s team wins, teams need approval for an interview, which has to take place before the divisional round.

No initial interviews can be requested or granted for candidates whose teams are still in the playoffs after the divisional round, i.e. anyone from the four teams vying for a conference championship.
— SB Nation, 1/10/17

Yeah, like this is faithfully adhered to.

Sad how the NFL’s so-called “anti-tampering policy” is respected more on the college coaching level than on it’s own, especially during what’s arguably the most important part of the season.

This is an unnecessary distraction inflicted by losing franchises on teams that should be preparing for the well-earned chance at the Super Bowl. This unfortunately happens and repeatedly every season as the teams contacting these coaches aren’t affected because they weren’t good enough to get past December.

The Patriots lost Super Bowl XXXI to the Packers after it was announced, the week prior, that their head coach would be leaving to coach the Jets. Could this have also affected the Vikings who got humiliated in the NFC Championship?

That was then; this is now….

Vikings offensive coordinator Pat Shurmur named head coach of Giants
Steelers Todd Haley is the new Browns offensive coordinator
Patriots offensive coordinator Josh McDaniels, Colts, Heading Towards Second Interview For Head Coach Position
NE special teams coordinator Joe Judge may join fellow departing Patriots assistant coaches

And can a coach effectively concentrate on two teams at the same time, one of his teams now in the Super Bowl?

Patriots defensive coordinator Matt Patricia, Soon-to-be Lions head coach, reportedly already letting assistants go

At the end of every National Football League, “Black Monday” is the prelude to the sabotage of those teams that were competent enough to make it to the playoffs. With nothing to lose, owners and team general managers begin that search for someone, anyone, to take their teams from perennial losers to playoff hunters. But by doing so, they’re interfering with the chemistry of a team now trying to concentrate on winning a Super Bowl and the losers could care less.

If a team can endure a 17-week season of mediocrity or worse, it can wait another five weeks until the best teams play towards that big game undisturbed by losers.

2018 UPDATE

It didn’t take more than a few hours after the official end of the 2018 regular season for the interference to begin anew.

Green Bay Packers expected to request permission to interview Patriots play-callers Josh McDaniels, Brian Flores

Again, teams that couldn’t complete the mission disrupting those in the current process of winning.