There were allegations of low pay and inadequate protection for workers at the height of the pandemic.
But Boohoo bosses say ensuring staff are looked after and respected, is something they take very seriously.
They've now opened a new factory in Leicester, built on the site of a former car showroom.
The company has a turnover of two billion pounds a year, and manufacturing is booming - and they say looking after staff is a key part of their success.
Andrew Reaney the Director of Group Product Operations, said that treating their staff properly was a minimum requirement.
He said: "Every single supplier we have undergoes a rigorous audit process.
"It's challenging at the moment, the minimum wage has gone up as we now know.
"Like any British business, you've got to work harder and you've got to work smarter and operationally you have to be really efficient."
In 2020, the fashion retailer hired barrister Alison Levitt QC to carry out a review after the allegations emerged about failings in its supply chain.
Ms Levitt said many workers were not aware of their rights and that the firm knew how they were being treated months earlier.
Boohoo said its business model is not founded on exploitation.
The company says important lessons have been learned since that report was first published and big improvements have been made.
Mr Reaney continued: "The report made for pretty painful reading, it's fair to say. We were very very open about the challenges that we had.
"We effectively didn't have the right structures, didn't have the right experience in place. We then went through what we call a regenerative change programme.
"Very proud again to say that our PLC board signed off on that programme about two months ago."
Hope for Justice, a charity set up to end human trafficking and modern slavery believes a significant number of factories in Leicester are still operating like sweatshops.
Tim Nelson, the CEO, says all companies need to carry out due diligence in manufacturing procedures to ensure workers are not exploited.
Tim says modern-day slavery must not be tolerated:
"We think it's important with all supply chains which are ever-moving and changing for everyone to do the right level of due diligence and care across all of their supply chains to make sure that this crime of modern day slavery and exploitation is not tolerated."
Boohoo says its new factory will be a centre of excellence, and it will share best practice with suppliers.
Analysis - Leicester's long history with the fashion industry
For decades, Leicester was known as the city that clothed the world.
It was an industrial powerhouse, famous for its textiles and hosiery firms.
Back in the 1930’s, it was named the second richest city in Europe.
Fast-forward to the 21st century, Leicester doesn’t enjoy the same prestigious reputation it once had.
Leicester’s textile factories aren’t as busy as they were in years gone by but big fashion retailer Boohoo is hoping to change that.
Bosses at the new manufacturing site on Thurmaston Lane in Leicester told me important lessons have been learned since the review and huge improvements have been made.
They said they carry out frequent checks on their suppliers to ensure staff are paid fairly and treated well.
There are thousands of textile firms in Leicester and many continue to operate like sweat shops.
I have interviewed workers who made clothes for big brands, not Boohoo, who described having to work long hours for low pay and in desperately filthy conditions.
One woman even told me she felt guilty asking for a toilet break.
Boohoo says it wants to lead the way, to show suppliers how they should operate.
Production at the factory is already underway and 180 jobs have been created.
It’s a positive move for the company and for the city - but, and it’s a big but, there’s still a long way to go before the sweatshops of Leicester become a thing of the past.
Take a look inside Boohoo's new factory: