A man from Lanarkshire has died from Legionnaires' disease after returning home from holiday in Bulgaria.
John Cowan, from Hamilton, died in June a week after falling ill at the Hotel Kalofer in the Sunny Beach resort.
The 43-year-old's family believe he contracted the airborne bacteria at the hotel and are threatening legal action against holiday firm Jet2.
Jet2 said two sets of independent tests had found no evidence of contamination at the hotel.
The flight and holiday operator confirmed two of its customers died shortly after returning to the UK from holiday in Bulgaria.
Mr Cowan's mother Marie, a retired care assistant, said: "When John came home he was feeling unwell.
"He was weak and his bones were aching.
"He basically stayed in bed most of that week - it wasn't until he started getting short of breath that we went to the GP.
"As soon as the doctor saw John he realised he needed urgent attention and phoned an ambulance which took him to Wishaw General."
Mrs Cowan said he was diagnosed with Legionnaires' disease at the North Lanarkshire hospital and his health deteriorated to the point that he went into cardiac arrest during surgery and died on 19 June - one week after returning from his holiday.
Mr Cowan's brother Barry said the family was preparing to take civil legal action because of what he claims is inaction on the part of Jet2 and the hotel.
He said: "We are all devastated.
"We just want answers - to know why this happened, to know it will never happen to anyone else and to know why the tour operator and the hotel have done nothing to help."
Mark Gibson, a partner at Digby Brown solicitors, said: "We are currently investigating a claim that a man died as a result of Legionnaires poisoning at a hotel in Bulgaria but as the case is at an early stage it would be inappropriate to comment further."
A spokesman for Jet2 said: "Sadly, we can confirm that two customers recently passed away shortly after returning to the UK from holiday in Bulgaria.
"We would like to offer our heartfelt condolences to their families at this very difficult time, and we have been in constant contact to offer all the assistance and support that we can.
"The health and safety of our customers is our absolute priority. In response, and to support our investigation, two independent specialists were instructed to take samples from the hotel and a United Kingdom Accreditation Service-accredited laboratory conducted testing of the water samples for any contamination.
"The results of all their tests were negative. We will continue to assist the local authorities in their investigations as required. "
The firm added that as a precaution it had, along with other UK-based tour operators, transferred all customers and all future bookings to other hotels in the resort.