There is concern people will spend longer in custody amid escalating strike action by court staff.

Staff at Auckland and Manukau District Courts are undertaking a ban on serving, checking and signing sentencing documents.

Criminal Bar Association President Len Anderson told Mike Hosking the backlog caused by the strike is causing problems for people in custody. 

"The courts are busy anyway so it has done is effectively for each day of sitting since mid-September you have had half a day carried over."

"So what happens is that people are being held in custody longer, bail is not being attended to, some people who would have been released on bail are being held in custody.

He said while it's an inconvenience for people on bail, it's a lot worse for those being held in custody. 

"If, for instance they were to be sentenced to home detention or a community-based sentence, they are going to spend longer in custody until their sentence date."

LISTEN ABOVE AS LEN ANDERSON SPEAKS WITH MIKE HOSKING