The route of London's £16bn Crossrail scheme could tunnel through a lost 16th Century anthrax burial ground.
The site at 10 Hayne Street, in the City of London, was due to be purchased by Crossrail through compulsory order powers on Friday.
But a Conservative peer, Lord James, warned: "We may very well have here at Number 10 Hayne Street a missing anthrax burial ground that has been lost for 488 years.
“Churches in the area refused to accept the bodies of the 282 victims of the anthrax outbreak that wiped out the whole population of Hayne Street at that time.”
There are also concerns that the Crossrail tunnelling may disrupt ancient plague pits.
Plague spores, like anthrax, can lie dormant for centuries but if disturbed can spread through the air.
During earlier site investigation work for Crossrail at Farringdon in May 2009, human remains were found in a deep exploratory bore hole in Farringdon, but they showed no traces of plague or anthrax.
Transport Secretary Lord Adonis said he accepted it was an issue that needed further study.
"Crossrail understands that there is a very small possibility of buried human remains being encountered during the works at 10 Hayne Street," he told peers.
But he said it was "highly unlikely that the works would release any anthrax spores or bacteria causing plague".