An internet service provider (ISP) says the Federal Government's proposed filter has the potential to cause bottlenecks and webpage blackouts, making its high-speed National Broadband Network less viable.

The Government announced the filter two years ago as part of its cyber safety program to protect children from pornography and offensive material. Last year it ran tests on the system.

John Lindsay from internet company Internode says such a filtering slowdown will make a big difference to businesses, especially when downloading files.

"It is mostly about lag. When you click on something it will add milliseconds... fractions of a second, probably in the order of a fifth-of-a-second lag to everything, but of more concern is what happens when something breaks in that mechanism," he said.

"Because it is a single, narrow path through which internet traffic has to flow you'll need lots and lots of filtering units and you'll need some mechanism for actually splitting the traffic up into these small chunks.

"It will add a lot of cost for ISPs and from everything that we have seen to date that is a cost that ISPs are expected to bear. So ultimately it will make broadband more expensive in Australia."

Google Australia support the Government's rollout of high-speed broadband, but the company's head of government affairs, Iarla Flynn, has serious questions about how the filter will affect internet connections.

"It is a question mark. We just don't know until... it is very difficult to say what the impact might be," she said.

"It would be a shame to tarnish the very, very positive story with the NBN with a filter which could have impacts but which also sends a negative signal about how development of the internet and use of the internet is seen here."

Geordie Guy from internet rights group Electronic Frontiers Australia says the Government may well have to retest the filter on the super-fast broadband speeds.

"The filter hasn't been tested with speeds like the NBN proposes to deliver. It has only been tested up to the types of speed that we expect to see today," he said.

"There is an awful lot of unlesses. I think it is probably getting to the point where the unlesses and the exceptions are getting to critical mass.

"We are probably starting to get around to the point where the Government needs to go right back to the drawing board, beyond the drawing board of a national technology response and see if this really is the best way to protect children online."