Telstra is embroiled in a controversy after NBN Co contractors found deadly asbestos in the pits they were working in.

Unions have weighed into the issue, calling for a halt to the NBN roll-out.

According to Dave Cox, many of these asbestos-lined pits can be found in the Illawarra.

Mr Cox worked for Telecom, Telstra's previous incarnation, for 23 years, finishing in 1982. He estimated that at the time he left, there were more than 7500 asbestos pits from Helensburgh to Gerringong.

"If you go further down the coast, into Nowra, there's even more," he said.

"There are thousands upon thousands of them.

"These things are everywhere. They're still there because Telstra doesn't do maintenance any more. Telstra only work on an as-required or as-necessary basis."

Mr Cox claimed many of them would still be in use today because "they form the backbone of the network to this day".

Contractors with NBN Co needed to access the Telstra pits to lay their cable. Mr Cox said this necessitated disturbing the asbestos.

"The NBN, they've got to install access for their optical fibre and a lot of these pits aren't big enough," he said. "So what they've got to do is knock them out or alter them to be able to take their NBN equipment. You've got to disturb the asbestos, you have no other choice. If you left it in the ground and didn't disturb it I don't think there would be a problem."

Mr Cox was part of a team whose job was to put in the asbestos pits. He said the asbestos used was the same as fibro and they wore no protective clothing.

"The engineering instructions, if you want to make a hole in an asbestos pit, you just use a hammer," he remembered.

"If you want to shorten a pipe or anything else, you use a blunt saw. That's what they used to recommend."

Mr Cox also said he had disposed of "hundreds" of broken asbestos pits at Helensburgh, Russell Vale, Wollongong and Unanderra tips.

"We took them everywhere, just broke them up and just threw them in a heap on the tip," he said.

"We didn't cover them up or bag them or anything else. Just broke them up and dumped them out the back of the truck."

Last week, Telstra chief executive David Thodey said the telco took full responsibility for the issue of the asbestos pits.

A Telstra spokesman said that as the network had been rolled out over a 100-year period, there were difficulties in determining where asbestos pits lay.

"Our pits that do contain asbestos were installed before the health issues associated with asbestos were known so no records of what the pits were made of were kept," the spokesman said.

"We haven't used concrete with asbestos for our pits since the mid-1980s. Our network includes millions of pits made from a variety of materials including plastic and concrete [that may or may not contain asbestos]."

The spokesman said that the pits posed no risk if left undisturbed.

However, should they have to carry out work on an asbestos-lined pit, Telstra workers followed a set safety procedure.

"It is only when the work at a pit requires it to be broken up or disturbed that workers need to follow strict safety procedures," he said.