Mary-Kate and Ashley Olsen have hit back after being sued by their former interns for ''wage theft''.

A lawsuit - filed in Manhattan Supreme Court - has been brought against the 29-year-old fashion designers' company Dualstar by interns, who claim they weren't paid for their work.

But in a statement to E! News, Dualstar called the allegations ''groundless'', explaining: ''As an initial matter, Dualstar is an organisation that is committed to treating all individuals fairly and in accordance with all applicable laws. The allegations in the complaint filed against Dualstar are groundless, and Dualstar will vigorously defend itself against plaintiff's claims in court, not before the media.''

The statement added: ''Dualstar is confident that once the true facts of this case are revealed, the lawsuit will be dismissed in its entirety.''

The lead plaintiff, former design intern Shahista Lalani, said in court documents that although the Olsens were nice when they came into the office of fashion label The Row, she was overworked by their head technical designer during her time there in 2012.

She said: ''They [Mary-Kate and Ashley] are really nice people. They were never mean to anyone. They're business people.

''[But the head technical designer] was very demanding. I was doing the work of three interns. I was talking to her all day, all night. E-mails at nighttime for the next day, like 10pm at night.''

The suit is seeking class action status and estimates up to 40 past and present interns could join.

Lalani added in the filed documents: ''When we weren't doing something, they'd be like, 'Organise the buttons in the back by colour code.' You don't get a set 15-minute break.

''You're like an employee, except you're not getting paid. They're kind of mean to you. Other interns have cried. I'd see a lot of kids crying doing coffee runs, photocopying stuff.''