BioInitiative proposed safety level of radiation:
0.01 millionth of a watt per centimetre squared
Natural level of radiation:
less than 0.000001 millionth of a watt per metre squared
In 2007, an international group of scientists studied 2000 peer-reviewed and published research papers.
They recommended an acceptable level of radiation of not more than 0.6 V/m = ~1μW/cm2 outdoors, and 0.2 V/m = ~0.1 μW/cm2 indoors, based on the interaction between low-level microwaves and the cellular processes.
This became known as the Bioinitiative Level,
which has since been lowered by a factor of 10, to 0.01 μW/cm2.
The New Zealand safety limit (NZ2772.1.1999) for the specific absorption of radiation from transmitters close to the body (ie cell phones) is 2W/KG over any 10 grams of body tissue. This standard is really based on protecting the body from heating effects, please check the New Zealand government information site.
See here for further comparison with other countries/states.