World 100 metres record holder Tim Montgomery and three other U.S. athletes accused of doping violations look set to be barred from IAAF Grand Prix meetings.

Nick Davies, spokesman of the International Association of Athletics Federations, said that under IAAF rules athletes in such a position were likely to be suspended even if they contested their cases.

Also Read Montgomery accused of doping World mark lifted Montgomery

The U.S. Anti-Doping Agency (USADA) are due to hold hearings with the athletes, who have not failed drugs tests but face allegations based on documentary evidence, and their lawyers within 10 days.

"They (USADA) will say to the athletes, 'right, we believe there's a doping offence on this day, our sanction is two years (ban)' or whatever they want to give them," Davies said.

"The question then becomes does the athlete accept, sign at the bottom of the certificate...or do they fight?

"If they fight they then have the right to the CAS (Court of Arbitration for Sport) hearing...and then they can be provisionally suspended."

Montgomery, among the favourites for August's blue ribband title at the Athens Olympics, received a letter from USADA on Tuesday accusing him of using banned substances.

Fellow top U.S. sprinters Chryste Gaines and Michelle Collins and 400 metres runner Alvin Harrison also received similar letters, according to Gaines' attorney and sources close to the investigation.

The allegations stem from a grand federal jury hearing into the operations of the Californian laboratory Bay Area Laboratory Co-Operative (BALCO) which is suspected of supplying a previously undetectable steroid, tetrahydrogestrinone (THG).

Davies said it was hard to go into details before the hearings.

"We've got letters that have been sent but we don't know what's going to happen when they meet, when they discuss," he said.

He added that the cases were to some extent "unknown territory" for the IAAF since such cases did not originate from failed drugs tests.

Davies said the athletes could be allowed to continue competing at IAAF meetings if the sport's world governing body rejected the USADA's submitted evidence but said that was unlikely.

Montgomery was due to run in Eugene, Oregon, on June 19 in the Prefontaine Classic. He was also tentatively expected to run in Stockholm in July, although the meeting promoter said last month that he would be unhappy to have him if drugs charges were still outstanding.

Montgomery and his partner Marion Jones, who is also being investigated, have vehemently denied any suggestion of cheating.

Montgomery's lawyers said he would fight any attempt to ban him from the Olympics.