Builders claim they are being held to ransom by their bosses and forced to go to work as pressure mounts on the Prime Minister to shut down all construction sites.
Mr Johnson was bombarded with calls to put a halt to all non-essential construction projects during Prime Minister's Questions yesterday.
But after London Underground trains and building site canteens were pictured packed with workers, employees have hit back saying they are being 'blackmailed' into going in.
One builder tweeted a video of a crowded site yesterday with the caption: 'How can this be happening and how can companies blackmail you to work. If you don't come in it's disciplinary or no money.'
The UK's main house builders Bellway, Persimmon, Barratt and Taylor Wimpey have all decided to stop working, but Redrow and Cairn Construction are still open. Work on the £18billion Crossrail project has also ground to a halt.
Last night the PM fell short of a complete ban, but warned workers to stay at home unless absolutely necessary - or more people will die.
Mr Johnson's decision to keep some sites open has resulted in a furious row with his successor as London Mayor, Sadiq Khan.
Prime Minister Boris Johnson is facing mounting pressure to shut down all construction sites over concerns about social distancing and spreading coronavirus. Pictured on Monday: A busy canteen for builders in London
A graphic shows which UK construction companies have shut down their sites amid the coronavirus pandemic
Mr Khan argues that while the London Underground should remain open for 'key workers', particularly those who work for the NHS, builders are taking up too much space on crowded Tube trains and should be forced to stay away.
He said yesterday: 'Construction workers are still going to work and using public transport.
'You can't keep a safe distance on sites so the virus will spread and more people will die. I've repeatedly asked ministers to ban non-essential work. We need action today.'
But Public Health England's chief medical officer Professor Chris Whitty backed the PM, saying there has to be a 'trade-off' when it comes to such decisions.
Professor Whitty said action on construction has to be sustainable, as measures could be in place for a number of months.
British house builder Taylor Wimpey has shut down all of its UK construction sites
Persimmon has also decided to stop UK developments to help stem the spread of the virus
He said: 'The modelling we have done was based on the idea that quite a lot of people would have to go to work as part of this.
'We have to remember that many of the things we have to do are going to have to be sustained for a reasonably long period of time.
'And broadly the more difficult you make it for people the less easy it is to sustain. So there is some degree of trade-off between those two things.'
At PMQs yesterday, Labour leader Jeremy Corbyn spoke of a self-employed construction worker who tested positive for the virus after being forced to travel to work by Tube.
He asked: 'Can the PM be absolutely clear and give unequivocal guidance now that construction work on non-emergency work should stop now?'
Shocking video footage shows more than 100 Laing O'Rouke employees packed into a crowded canteen at the site of the new Royal Hospital in Liverpool yesterday
Mr Johnson replied that some construction sites should continue to operate as long as social distancing - keeping six feet apart - is maintained.
A Number 10 spokesman later added that 'further steps' could be implemented as time goes on and that 'nothing is off the table' when it comes to COVID-19.
It comes after the Mayor of Liverpool slammed developers Laing O'Rourke for failing to implement social distancing.
Shocking video footage shows more than 100 Laing O'Rourke employees packed into a crowded canteen at the site of the new Royal Hospital in Liverpool yesterday.
Builders are seen sitting close together on small tables as they chat, eat their lunch and play on their mobile phones.
The new Royal Hospital is being built next to the current Royal Liverpool University Hospital by the same developers responsible for the London Olympics buildings in 2012.
Earlier this week Laing O'Rourke company bosses said they wanted to 'protect' their workers from the spread of coronavirus as the death toll reached 465 in the UK.
In London, Mayor Sadiq Khan argues that while the London Underground should remain open for 'key workers', particularly those who work for the NHS, builders are taking up too much space on crowded Tube trains (Central Line at White city seen on Wednesday) and should be forced to stay away