Update: The NFL apparently means business too as it informed all 32 teams to keep their phone records from the three-day tampering period for review as part of the investigation, according to Adam Schefter.
The NFL plans to investigate the violation of free agency rules by multiple teams after terms of contracts were reached prematurely, according to Rand Getlin of Yahoo Sports.
In 2013, the NFL added a three-day "legal tampering" period that allowed teams to negotiate with agents prior to the beginning of free agency. According to the new rules, teams could negotiate, but no contract terms could be agreed upon until after 4 p.m. on the Tuesday when free agency begins.
Several top 2015 free agents have already agreed to contract terms with more than a day until the free agency period begins. Among the premature contract announcements so far are deals reportedly in place for Ndamukong Suh, Byron Maxwell, Pernell McPhee and Jeremy Maclin.
SB Nation presents: How the NFL's legal tampering period works
That hasn't sat well with the NFL, which sent all 32 teams a letter voicing its disapproval. The full email, via Albert Breer of NFL Network:
Clubs were advised of the rules for the three-day negotiating period in PP-23-15 (attached). These rules include limitations such as that a club cannot make an "offer;" or enter into a written or oral agreement of any kind, express or implied, or make promises or representations of any type concerning the terms or conditions of employment to be offered to any Unrestricted Free Agent for inclusion in a Player Contract after the start of the new League Year; or provide assurances of intent as to the future execution of an NFL Player Contract. Clubs were further advised that "Any attempt to undermine the purpose of this negotiating period may be considered conduct detrimental to the League." At this time, the League office is beginning investigations into a number of reported agreements with clubs. Violations will be dealt with accordingly.