The Telecommunications Users Association (TUANZ) fears the sharp drop in mobile-phone termination rates recommended by the Commerce Commission will not be passed on to consumers.
In a draft decision released on Thursday, the commission says mobile termination rates - what companies charge for switching voice calls between their networks - should be slashed from 17c to 4.7c a minute by 1 April, with further reductions to 3.9c by 2014.
It also says the text termination rate should be eliminated.
TUANZ's business development manager, Katherine Hall, says the reduction should be implemented immediately or no later than 1 April as proposed.
"There's a danger that the rate will fall and yet we will not see the pass-through," she says, "and for us it's really important that this happens sooner rather than later."
Pressure can be put on the phone companies, Ms Hall says, "if every consumer out there votes with their wallet".
Vodafone says Telecom will pocket any gain
Vodafone says the Commerce Commission cannot assume that slashing the rate will translate into lower prices for users.
Its general manager of public policy, Hayden Glass, says overseas evidence indicates Telecom will pocket any gain, rather than consumers.
The commission says, however, that lower mobile termination rates will promote competition, particularly for new entrants like Two Degrees, and that in turn will benefit consumers - and Two Degrees chief executive Eric Hertz agrees.
"They've already reacted to our price competition in the marketplace," he says, "and I think that they would continue to do that."
The companies will get a chance to comment on the commission's recommendations before a final decision is released in March.