Ten people died when a police helicopter crashed into the roof of the Clutha pub on November 29 last year.
More than 100 people were inside the city-centre bar at the time.
Irwin Mitchell's specialist aviation law team has sent a letter of claim to the legal representatives of Bond Aviation Group and also reiterated calls for a full examination of what can be done to improve helicopter safety.
One client the firm is representing in the claim is John McGarrigle. Mr McGarrigle's father, also called John, died when the helicopter crashed through the bar's roof.
It has not yet been established what caused the helicopter to fall from the sky.
Irwin Mitchell partner Elaine Russell said: "We have now issued a letter of claim to Bond Aviation Group which, as the owner and operator of the aircraft, is legally liable."