"The document basically says 'They [the UK and Australia] are going there' - so why aren't we?," he said.
Robertson was also critical of the timing of the measure, following nearly a year of public debate about the issue.
"We're doing to have a discussion document released next year, so there's no way they'll be able to make te required legislative changes before the election. This is an effort by government to park this up as an issue," Robertson said.
"That won't work: We won't let them. We want to have a conversation during the election campaign about whether everyone is paying their fair share of tax."
Green Party co-leader James Shaw echoed these criticisms. "Better late than never is my first reaction. It's a bittersweet moment: This has taken them forever, and it doesn't go far enough," he said.
Shaw said digital companies with only a virtual footprint in New Zealand would not be caught up in the proposed crackdown and this unresolved problem needed action.
"When this story blew up in March, a lot of the public concern was about companies like Google and Apple who have a huge commercial presence in New Zealand and yet pay next to no tax."
Shaw said a diverted profits tax would act a signal to both these companies and to the wider public that the government took the problem seriously.
"A lot of people are asking 'If they don't pay tax, why should I?' It leaks through to the rest of the economy and undermines confidence in the system."
The business community this morning also began to weigh in on the debate, with umbrella group Retail NZ saying more action was needed to extend GST to cover online sales shipped into the country.
Retail NZ's spokesman Greg Harford, said: "New Zealand-based firms selling online or in retail shops have to charge up to 25 per cent more than big foreign retailers, and this costs the Government at least $200 million in lost revenue. Fixing this loophole is a no-brainer, and easy to do."