All three players vehemently denied refusing to provide a sample and terminated their contracts on June 1, immediately before they were due to appear before a Bath disciplinary hearing.
The RFU statement read: "The RFU, and our partners at Premier Rugby, work tirelessly to ensure the reputation of the game is protected.
"The RFU have now completed their initial investigations into the allegations made against former Bath players Justin Harrison, Michael Lipman, Alex Crockett and Andrew Higgins.
"We can confirm we will be asking the players to appear before an RFU disciplinary panel charged with conduct prejudicial to the interests of the Game on a number of charges including taking prohibited substances and wilful refusal to take a drugs test.
"All details of the investigation now form part of the disciplinary process and to protect the integrity of the process will remain confidential.
"The RFU will make a further announcement when the panel has been convened and a date has been set but can confirm we intend to call a number of players, club management and other third parties to appear before the panel to support the case."
Source: AFP European Edition