Alleged breaches of anti-doping rules were Friday levelled against 34 Australian Football League players following a 16-month investigation.
The Australian Sports Anti-Doping Authority (ASADA) said the decision to make formal allegations of possible violations was based on considerable evidence.
"Following the conclusion of joint interviews with the AFL in mid-2013, ASADA continued to accumulate evidence to establish a possible violation," said ASADA chief executive Ben McDevitt.
"Based on the advice of our legal counsel and a review of the evidence ... I have reached the conclusion that these players have a case to answer under the World Anti-Doping Code," he said.
The players, accused of using a prohibited substance, were not named but media reports said they were past and current footballers from top side Essendon.
The substance was also not mentioned but reports have suggested it was a peptide thought to aid recovery from injury.
Essendon were not immediately available for comment but chairman Paul Little was expected to publicly respond later Friday.
The same club was last year hit with the biggest fine in the sport's history and coach James Hird banned for 12 months for bringing the game into disrepute over a drug supplements scandal.
As well as being slapped with the Aus$2.0 million (US$1.8 million) penalty, the Bombers were kicked out of last year's finals series.
The 34 players have 10 days to lodge their responses. That information, along with the evidence collected by ASADA, will then be put to the independent Anti-Doping Rule Violation Panel for consideration.
"Our priority is to ensure that Australian sport is clean and the health of athletes is protected," said McDevitt, vowing to investigate any possible instance of doping.
"We want athletes to feel confident when they take to the arena that they are competing on a level playing field."