Tour de France winner Alberto Contador and Michael Rasmussen are not welcome to race at this month's Hamburg Cyclassics, organisers have said.
Contador has never failed a doping test and denies any wrongdoing
Contador cannot take part because his name has been connected to the Operation Puerto blood doping scandal, though he was cleared of wrongdoing.
Rasmussen was barred after his Rabobank team sacked him for missing drugs tests and lying about his whereabouts.
Meanwhile, Astana's Andrej Kashechkin has tested positive for blood doping.
He is the second Kazakh rider from the team to test positive for a blood transfusion after star Alexandre Vinokourov was thrown out of the Tour for the same offence.
This new, hard blow does nothing but reinforce the will of the Astana Cycling Team's management to set up drastic measures for a clean cycling
As a result, the entire team withdrew from the blue riband race and Vinokourov was subsequently fired.
Kashechkin has been suspended by Astana until the results come through from his 'B' sample.
"This new, hard blow does nothing but reinforce the will of the Astana Cycling Team's management to set up drastic measures for clean cycling," the team said in a statement.
Cycling is once again trying to clear up its image after the sport was rocked by yet more high-profile drugs scandals at this year's Tour de France.
Organisers of the Hamburg race are trying to distance themselves from further drama.
Managing director of the race Frank Bertling said: "Our basic position is that we don't want to have any riders in the Hamburg race who are on the Fuentes list."
That list is said to include over 50 professional cyclists who were connected with a blood doping investigation, named Operation Puerto, in Spain.
Eufemiano Fuentes is the doctor said to have masterminded doping programmes for athletes.
Police raids in Madrid and Zaragoza last year uncovered large quantities of anabolic steroids, laboratory equipment and more than 100 bags of frozen blood.
Contador plans to make a prepared statement on Friday, though it is unclear what he plans to say.