The allegations are the result of Australian Sports Anti-Doping Authority's protracted investigation into the possible use of banned substances in sport.
"The Australian Sports Anti-Doping Authority (ASADA) today issued amended 'show cause' notices to 34 former and current Essendon football players for the use of a prohibited substance, Thymosin Beta 4, during the 2012 season," a statement issued by ASADA read.
Thymosin Beta 4 is a peptide hormone which promotes growth, the use of which is banned under the World Anti-Doping Agency (WADA) code.
The players had already been issued with show cause notices in June but the cases were put on hold pending a legal challenge to the ASADA probe in the Federal Court precipitated by an injunction served by the Australian Football League (AFL) club.
Essendon coach James Hird, who recently completed a 12-month ban issued by the AFL for bringing the game into disrepute, has also undertaken legal action.
"The resumption of action against the players follows the Federal Court's dismissal of the applications by the Essendon Football Club and James Hird on 19 September 2014," read the ASADA statement.
"Notwithstanding James Hird's appeal of the Federal Court decision, ASADA has agreed to a formal request by the legal team for the bulk of the players to expedite the 'show cause' notice process."
The players have 10 days to respond to the notice, although ASADA said they would be sympathetic to requests for extensions to that period given the evidence totals some 350 pages for each case.
The ASADA probe was triggered by a dramatic news conference by the country's then sports minister in February 2013 on the back of a report that alleged, among other things, the widespread use of banned substances in Australian sport.
The investigation also found wrongdoing in the top-flight National Rugby League, with 17 players accused of using banned substances when playing at the Sydney-based Cronulla Sharks in 2011.
In August, 12 current and former Cronulla players accepted one-year bans from ASADA, which were controversially backdated to Nov. 2013, ensuring that most of them would only miss a handful of regular season games.
Essendon's players, having already rejected an offer to cut a deal with ASADA, are unlikely to receive similar lenience.
(Reporting by Nick Mulvenney; Editing by John O'Brien)
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