The crackdown on XL Bully dogs comes into force today meaning the breed must be kept on a lead and muzzled in public while breeding, selling and abandoning them is also illegal.
Animal welfare groups fear the ban will overwhelm rescue centres and vets - with hundreds of the dogs set to be put down this week.
Owners have been urged to apply for a certificate of exemption for current pets before the January 31 deadline.
It will be a criminal offence to own an XL bully dog in England and Wales without a certificate from February 1.
Environment Secretary Steve Barclay said the Government had met its pledge to take 'quick and decisive action' following a series of attacks, with one man dying after being savaged by one of the dogs earlier this year.
But the RSPCA said the measures were 'not the answer' and warned of a 'huge risk' that rescue centres and vets will be unable to cope with the likely surge in demand.
The crackdown on XL Bully dogs comes into force today meaning that selling the breed is illegal
A horror Bully type dog attack occured in Mansfield
Samantha Gaines, dog welfare expert at the charity, said: 'What is really concerning is because the ban has come in at such a pace that there may be owners who are not ready for this, being able to ensure their dog is happy wearing a muzzle.
'There is some fear that people for whatever reason may have left it a bit late and about what that means.'
She added: 'Breed is not a good or reliable predictor of aggressive behaviour.
'Whether or not a dog goes on to use aggressive behaviour depends on how they've been bred, how they've been raised, their life experiences.'
Instead of targeting dogs with new laws, Dr Gaines said existing legislation should be used more effectively to clamp down on people who exploit and irresponsibly breed the animals.
And she warned against 'misleading the public that they're going to be safer when really we have to tackle root causes'.
Owners are selling their XL Bullys for as little as £10 on the internet in a desperate bid to get rid of them
Another owner is giving up their female XL Bully for free to try and get rid of the dog
A one-year old XL Bully has been put up for sale on Facebook for £200
People on X are also trying to sell off their XL Bullies, with an entire litter available to purchase
Another dog owner put an urgent appeal up on Facebook giving away their dog for free
Meanwhile, the Association of Dogs and Cats Homes (ADCH) warned of increased abandonment rates and said the new rules may lead to a 'postcode lottery' for vets being able to help owners meet the terms.
To qualify for an exemption certificate, owners must prove their XL bully has been neutered by June 30.
If the pup is less than a year old by January 31, they must neutered by the end of 2024, and evidence must be provided.
As well as neutering their animals, XL bully owners seeking an exemption must also pay an application fee, hold active public liability insurance for their pets and ensure the dogs are microchipped.
The Department for Environment, Food and Rural Affairs (Defra) said a 'staggered approach' had been taken to the restrictions in order to safely manage the existing population of XL bully dogs while ultimately banning the breed.
The dogs were added to the Dangerous Dogs Act on October 31, giving owners two months to prepare for the first stage of restrictions.
People with dangerously out of control dogs can be jailed for 14 years and banned from owning animals, and their pets can be put down.
Mr Barclay said: 'The Prime Minister pledged to take quick and decisive action to protect the public from devastating dog attacks with measures in place by the end of 2023. We have met that pledge - it is now a legal requirement for XL bully dogs to be muzzled and on a lead in public.
It is also now illegal to breed, sell, advertise, gift, exchange, abandon or let XL bully dogs stray.
'All XL bully owners are expected to comply with the law and we will continue to work closely with the police, canine and veterinary experts, and animal welfare groups, with further restrictions on XL bully dogs coming into force on February 1.'