A law firm representing travellers is taking the government to court over the UK's quarantine hotel policy.
Passengers must spend 11 nights in a quarantine hotel on returning from red list countries, even if fully vaccinated and testing negative for Covid.
London-based firm PGMBM said it had called for a judicial review into the policy, but the government had refused.
The cost of staying in a quarantine hotel is now £2,285.
More than 60 locations including Turkey, Mexico, Kenya and many countries in Africa and Latin America are currently on the red list.
The other European countries with mandatory quarantine involving hotel detentions - Ireland and Norway - have amended their schemes so fully vaccinated travellers are exempt from needing to quarantine.
If PGMBM's claim was successful, not only would double-vaccinated travellers no longer have to quarantine at the hotels, but the government could also be forced to refund the fees of all those who were vaccinated and still had to stay there.
It is estimated more than 100,000 people have been forced to quarantine in hotels since the policy came into force in February this year.
PGMBM said it was launching a legal case, representing "multiple" clients. It described the policy as an "unlawful deprivation of liberty" that violated fundamental human rights.
It is now asking anyone who was forced to stay in hotel quarantine to register their details and help form a class action aimed at forcing the government to reverse its policy.
One of the firm's clients, Ozgur Akyuz, a bus driver from Hackney, said his pregnant wife and three-year-old daughter caught Covid while staying in hotel quarantine two weeks ago.
"They were put in a hotel near Heathrow and it was filthy. She was crying all day long," he said.
"She saw a rat in her room and kept being served bacon and sausages, even though she told them she didn't eat pork.
"I ended up cooking food at home to take to her, and I also bought a rat trap from B&Q to give her peace of mind because the hotel did nothing."
Mr Akyuz said both his wife and daughter tested positive for Covid on the third day of quarantine, despite having tested negative when they left Turkey.
"They were allowed home after 10 days but I then caught Covid from them. So we have all had it. If she had come home to quarantine, chances are none of us would have got it."
The government has said it has taken "decisive action" to protect the country, including the quarantine system. Other countries around the world had taken equivalent action, it said.
This is the second case PGMBM has brought about quarantine hotels. The first was on the grounds of financial hardship and resulted in the government offering the option to pay in 12 monthly instalments for those facing financial hardship.