Regulators deciding whether Central Maine Power will get a key permit needed to build a 145-mile transmission corridor have extended their process into March.

The Maine Public Utilities Commission ruled Friday that it expects to extend the time for research, testimony and hearings into January, with a date of March 1 now set to wrap up the information-gathering aspect of the permit process.

The PUC is considering whether to award a certificate of public conveyance and necessity, a necessary component of CMP’s plan to deliver hydropower from Quebec to markets in Massachusetts.

The $1 billion proposal has drawn widespread interest and generated more than 300 separate filings and a similar number of public comments in the case. Multiple requests for complex technical data, as well as confidential negotiations aimed at settling narrow aspects of the case, were still in play last month.

Opponents of the plan successfully argued that they and the PUC needed more time to thoroughly vet all the information CMP provided in response to questions about the project. More than 90,000 documents were submitted.

In its order, the PUC said there were questions around engineering and reliability issues, calculation of environmental benefits, and pending legal settlements that needed more time, among other things.

CMP had hoped to have its permit from the PUC by the end of the year. A company spokesman said the delay from the PUC should not affect the planned timeline to begin construction of the project late next year or early 2020.