More than 100 people were in the Clutha bar in Glasgow's Stockwell Street when a police helicopter crashed through the roof on November 29.
Three people in the aircraft were killed as well as a further seven in the pub.
A specialist aviation team from law firm Irwin Mitchell has now sent a letter of claim to the legal representatives of Bond Aviation Group, the owner and operator of the helicopter involved.
It has also reiterated calls for a full examination of what can be done to improve flight safety.
The law firm was not able to disclose how many clients it was representing in the case, but confirmed it was acting for both injured victims and families of the deceased.
One client represented in the claim is John McGarrigle, whose father, also called John, died when the helicopter crashed through the roof.
Elaine Russell, a partner in Irwin Mitchell's Glasgow office, said: "Our clients have faced a difficult and traumatic time across the Christmas period after losing loved ones in the Clutha tragedy and we continue to eagerly await further information from the Air Accidents Investigation Branch regarding the progress of its investigations.
"We have now issued a letter of claim to Bond Aviation Group, which, as the owner and operator of the aircraft, is legally liable for the deaths of the police passengers and the ground victims in the pub, as well as those who were injured in the pub, under a legal concept known as strict liability.
"The response from the Glasgow community has been heart-warming and there are many fundraising efforts taking place to help those affected. We are absolutely determined to ensure that those who lost relatives in this crash not only get the financial support they may need following the incident, but also the answers they are desperately seeking."