Australia's competition regulator voiced objections on Tuesday to the proposed split of dominant phone company Telstra Corp, threatening to delay an historic reform designed to wire up the entire nation to high-speed broadband.

Telstra recently hammered out an agreement to hand over its fixed-line telecoms infrastructure, including cable ducts, to a state-run company for use in the government's $38 billion project to build a high-speed national broadband network.

The Australian Competition and Consumer Commission (ACCC)said Telstra's separation plan could not go ahead in its current form and called for important changes.

The ACCC's preliminary view is that Telstra's undertaking cannot be accepted in its current form and that important changes are required, it said in a statement.

Telstra, whose shareholders are due to vote on the separation plan on October 18, was taken by surprise, telling Reuters that it had not seen the regulator's statement and would review it before making a comment.

Telstra shares fell on the news, down 3.6 percent at A$2.96.

But fund manager Theo Maas, of Arnhem Investment Management, felt the regulator's intervention meant a delay rather than derailment of the reform, noting that the concerns focused mainly on the transition period during which Telstra would hand over its fixed-line assets to the new network.

The concern still lies on the road toward the National Broadband Network, he said.

With NBN being a 10-year process, Telstra will have reasonable power to disadvantage competitors from access to their old copper network during the roll-out period.

All in all, it won't stop the process but delay it slightly. Telstra's shareholder vote, too, may be delayed but Telstra could still go with it on schedule even before ACCC approval, if its negotiations with the regulator are close to finalising.

(Reporting by Mark Bendeich and Narayanan Somasundaram in SYDNEY and Sonali Paul and Victoria Thieberger in MELBOURNE; Editing by Ed Davies)