Opposition against the expansion of Waikeria Prison was taken to the steps of parliament yesterday.

The rally was led by a prisoner advocacy group that calls on the government to take steps to reduce the prison population and provide better alternatives.

The government is planning to build a new 600-bed unit at Waikeria Prison.

The Corrections Minister Kelvin Davis says it's the only option because the current facility at Waikeria is getting too crowded.

"Kāore e kore e tipu ake, e kake ake ana te nama o ngā tāngata kei roto i ngā whare herehere, nā reira mō tēnei wā me hanga tēnei, he whare herehere hōu. Tō mātou hiahia kia ritāia ai ngā whare herehere tawhito."

But mental health expert Dr Keri Lawson-Te Aho says she doesn't agree with what he says.

"That argument is nonsense and it's based on mythology about increasing the incarceration of our whānau."

Dr Lawson-Te Aho says people for example suffering mental illness should not be incarcerated.

Only time will show if the government will listen.