Construction workers are required to hold a CSCS card to prove skills and a knowledge of health and safety.
But a joint BBC London/Newsnight investigation found organised cheating.
Carl Rhymer, of the Construction Industry Training Board (CITB), one test provider, said 6,000 card-holders would be required to re-sit the exam.
CSCS (Construction Skills Certification Scheme) cards are widely seen as the UK's flagship scheme for certifying builders and are required by nine of the UK's biggest construction companies as well as Crossrail and Heathrow.
But the investigation found numerous test centres were offering guaranteed passes for cash, enabling workers lacking English to obtain qualifications and entry to dangerous construction sites.
During the investigation the BBC exposed Wep HSE, in Ealing, after its award-winning director, Garet Estensen, read exam answers from a big screen, instructing candidates: "Follow me on screen, guys. I'm going to shout the correct answer."
Confronted with the evidence, Mr Estensen made no comment.
The other two centres exposed during the investigation were Future Training 4 Jobs in Ilford and Training Xpress Limited in Colindale. Both have now been suspended from testing.
Mr Rhymer, director of delivery and customer engagement at the CITB, said it was aware of fraudulent incidents and was "tackling this head-on".
He said: "We are working hard with CSCS and the police to crack down on fraud and we are accelerating existing plans to install mandatory CCTV in all testing centres.
"We've also increased the number of spot checks on centres, to act as a deterrent."
Mr Rhymer said following a review it had found the "vast majority" of tests were legitimate but it would "require 6,000 individuals to be retested... to eliminate any doubt".
But Alistair Donaghey, health, safety and environmental manager of Willmott Dixon, a construction company with a Â£1bn turnover said: "I'll never trust the scheme again."
Those required to re-sit the test will be issued with vouchers to cover the cost at the CITB's expense, it said.
More than 6,000 builders issued with industry certificates will have to re-sit exams after the BBC uncovered the rigging of health and safety tests.