NFL spokesman Greg Aiello said the discussions are focused "on a full resolution of any remaining issues, including the role of a population study."
The labor agreement that ended the NFL lockout in 2011 requires the league gain union approval before testing players for HGH. The union says it favors testing, but has reservations about the appeals process.
The union also has reservations about the way discipline will be handed out, and wants to collectively bargain that issue.
Supplemental HGH is a banned substance that is hard to detect and used by athletes for what are believed to be a variety of benefits, whether real or only perceived such as increasing speed and improving vision.
Among the health problems connected to HGH are diabetes, cardiac dysfunction and arthritis.
In the union's email, it told the players that Dr. Alan Rogol has been jointly hired by the NFLPA and NFL to oversee the study and supervise two jointly retained biostatisticians. One of those biostatisticians, Donald Berry, will design the study protocol and conduct the analysis. The second will independently review both the protocol and the analysis.
In January, Major League Baseball and the players agreed to HGH blood testing throughout the regular season and to have a World Anti-Doping Agency laboratory in Canada keep records of each player.