A spat over doors in Parliament has led to accusations that Labour is lying.

Doors will soon be put in to separate Labour and National offices, across what's become known as Parliament's "demilitarised zone".

National MP Judith Collins says they're costing $30,000, and aren't necessary.

She says Labour's insisting on the doors, something denied by the party's chief whip Chris Hipkins.

Now Collins has produced an email from January 29 to prove her case.

"Well I think it is pretty clear evidence, so I think Chris Hipkins isn't being quite full in his explanations."