The New Zealand Herald understands staff expect up to 1000 jobs to go at the telecommunications company, and an announcement is expected today.
A Spark spokesman said that was not the case, but the company was always undergoing change.
"At a company of our size operating in such a fast-changing industry, there's always change going [on] within some areas of Spark."
He said the company's policy was that it did not comment on business decisions that affected its staffing numbers.
"We disclose our staff numbers on a bi-annual basis as part of our financial reporting and we don't tend to comment beyond this."
Spark's staff numbers have risen in the last year.
In December 2016 it had 5943 full time workers, up from 5324 in December 2015.
Spark reported earnings before interest, tax, depreciation and amortisation of $471 million in the six months to December 31, up from $455m in same prior period.
The spokesman said the technology world in which Spark operated was changing faster than ever before.
"As a consequence, our business has changed enormously in recent years and the one thing we can say for sure is that it will continue to do so.
"Our customers expect us to be offering the best deals at ever better prices, improving their service experiences and making it easier and simpler for them to use our products and services and to get help from us.
"That means as a business we must do even more to tightly manage our operating costs and radically simplify our products, tools and processes, taking advantage of the latest and best digital technologies."
