The group were due to perform at the Indiana festival on August 13 just before strong winds of up to 60mph caused the stage to collapse, killing 7 people and injuring over 45.
More than 40 people are suing the duo, claiming that they could have prevented the disaster by cancelling the show in advance, according to TMZ.
The suit's document claims that the band "failed" to use their authority to cancel the gig, having known about the poor weather conditions beforehand.
The lawsuit is also seeking damages from concert promoter Live Nation, ESG Security and the stagehands' union over the incident.
Sugarland staged a free memorial concert last month at the Conseco Fieldhouse in Indianapolis in honour of those who died.
> Sugarland on Indiana stage collapse: 'It tested our faith'