Tube maintenance firm Metronet has ordered immediate safety checks on its storage facilities on the network after a train derailed during rush hour.
Hundreds of passengers were stranded and 11 were taken to hospital when three carriages came off the rails on a westbound Central Line Tube train.
Transport for London said it had previously expressed concerns about the storage of equipment by Metronet staff.
People heading home faced long delays on parts of the Central Line.
The incident took place between Mile End and Bethnal Green stations in east London just after 0900 BST.
Services are suspended between Leytonstone and Liverpool Street, and there are delays on the rest of the line.
Mile End and Bethnal Green stations are also closed.
Transport for London (TfL) said it hoped the affected route would be operating by Friday afternoon.
TfL said the derailment was caused by a "roll of tarpaulin" which became dislodged from its storage recess inside the tunnel.
About 700 people were taken off the derailed train, and another stuck behind it, by about 1100 BST after a two-hour wait, it said.
In November 2006 a train struck a corrugated metal sheet left on the line and in May this year a similar collision occurred involving a plastic water butt.
Speaking to BBC London 94.9 Howard Collins, of TfL, said: "We are very concerned about storage. We have on several occasions spoken to Metronet about these previous incidents mentioned.
"We have carried out a formal investigation and we treat this very seriously."
Metronet has ordered an immediate review of all similar storage sites used by staff and contractors which is to be completed before the start of services on Friday morning.
A spokesman said: "Our initial reports suggest that a bale of material became dislodged from its licensed storage position in a tunnel cross-passage.
"As a precaution, Metronet has ordered an immediate audit of all similar storage sites used by its staff and contractors."
The Rail Accident Investigation Branch has launched an investigation.
The Rail Maritime and Transport Union (RMT) said this was the fourth such incident in 18 months and that they had warned about safety issues in the same area where Thursday's incident occurred.
A total of 37 people received medical treatment, including 11 who were taken to hospital with minor injuries such as panic attacks and breathing problems.
Chris Christofi, who was on the derailed Tube, said: "We felt a massive jolt underneath the train which caused the train to move up and down and sideways.
"There were some windows that seemed to blow in and explode and there was some soot that came into the carriage.
"There were a lot of people crying and upset, a lot of people falling over. We thought there'd been a bomb."
A spokesman for the union said that in May 2007 a central line train near Mile End struck a metal chest used by Metronet to store tools overnight and that this should have been secured away.
The driver stopped the train without it derailing, but was said to have been left in a traumatised state by the collision.
As a result the RMT wrote to London Underground demanding an inquiry.
"It's a miracle that the train did not derail then as well," the spokesman said.