http://www.nzta.govt.nz/resources/rules/glazing-windscreen-wipe-and-wash-and-mirrors-1999.html#31

Windscreens

3.1(5) Modifications to a windscreen must not unreasonably impair the driver’s vision and must comply with the following:

(a) except as specified in 3.1(5)(b), 3.1(5)(c) and 3.1(5)(d), overlays must not be applied to the glazing;
(b) stickers may not be applied, except if allowed or required by or under any Act, regulation or rule, unless they are wholly within:
(i) 100 mm from the top or bottom edges; or
(ii) 50 mm from the side edges;
(c) an anti-glare band overlay may be applied if:
(i) the anti-glare band overlay does not extend below the bottom edge of the vehicle’s original equipment specification sun visors when they are folded down as far as possible towards the windscreen; and
(ii) the anti-glare band overlay does not contain any print below a line that is 100 mm below, and parallel to, the top edge of the windscreen;
(d) a stoneguard overlay may be applied if:
(i) the vehicle is of Class MB, MD1, MD2, MD3, MD4, ME, NA, NB or NC; and
(ii) the overlay is applied along the bottom edge of the windscreen to a height that is not greater than the highest point of the steering wheel;
(e) radio antennae may be fitted only if they are wholly within 100 mm from any edge of the glazing.

Front side windows

3.1(6) Modifications to front side windows (that is, glazing forward of the left or right of the driver’s seatback in its rearmost and upright position) must not unreasonably interfere with the driver’s vision and must comply with the following:

(a) transparent overlays may be applied only if the overall visible light transmittance of the glazing is not reduced to less than 35%;
(b) stickers may not be applied, except if allowed or required by or under any Act, regulation or rule, unless they are wholly within:
(i) 100 mm from the bottom edge; or
(ii) 50 mm from the top or side edges;
(c) radio antennae may be fitted only if they are wholly within 100 mm from any edge of the glazing.

Rear side windows and rear windows

3.1(7) Modifications to glazing directly behind, or to the left or right of the rear of, the driver’s seatback in its rearmost and upright position in Class MA vehicles, except stretch limousines and body transfer vehicles, may be carried out as follows:

(a) transparent overlays may be applied only if:
(i) the overall visible light transmittance of the glazing is not reduced to less than 35%; and
(ii) the vehicle is equipped on both sides with rear-view mirrors;
(b) stickers may not be applied, except if allowed or required by or under any Act, regulation or rule, unless they are wholly within 100 mm from any edge of the glazing;
(c) radio antennae may be fitted only if they are wholly within 100 mm from any edge of the glazing;
(d) electrically-heated demister units may be fitted.

3.1(8) Modifications to glazing directly behind, or to the left or right of the rear of, the driver’s seatback in its rearmost and upright position in vehicles of classes other than Class MA, but including stretch limousines and body transfer vehicles, may be carried out as follows:

(a) overlays and other modifications may be applied only if the vehicle is equipped on both sides with rear-view mirrors;
(b) stickers may be applied anywhere on the glazing, but the vehicle must be equipped on both sides with rear-view mirrors if a sticker is not wholly within 100 mm from any edge of the glazing;
(c) radio antennae and electrically-heated demister units may be fitted.

Sunroofs

3.1(9) Modifications to the glazing of a sunroof may be carried out as follows:

(a) overlays may be applied;
(b) stickers may be applied anywhere on the glazing;
(c) radio antennae and electrically-heated demister units may be fitted.