The Whyalla steelworks has entered a series of shutdowns of its blast furnace due to an inability to source enough coking coal, according to an email obtained by ABC News.

The email, sent last Thursday, revealed the steelworks was expected to run out of coking coal on August 26, with the next shipment due to arrive in early September.

"When the coke runs out, we will shut the furnace down until the next coke shipment is onsite and partially discharged," the email said.

The email slated a 20-hour shutdown for last Friday to stretch current stocks, on the same day 48 people were axed from the company.

It also forecast another 20-hour shutdown for this coming Thursday, August 22.

In a statement provided to the ABC this morning, a spokesperson for steelworks owner GFG Alliance said that the company had since secured coking coal from a major competitor.

"This interim measure enables steelmaking to continue with minimal disruption, with a short hot idle for a few days."

The coal-fired blast furnace was knocked offline for three-and-a-half-months earlier this year after it cooled too much following a planned 48-hour shut down for maintenance.

During that time, hundreds of workers were forced to take a pay cut of about 30 per cent.

Last week, ABC News also revealed GFG Alliance owes several contractors in Whyalla tens of thousands of dollars.

Some businesses have warned they may soon be forced to lay off staff or go into liquidation.

None of the suppliers were willing to speak publicly for fear of impacting their relationship with GFG Alliance.

On the condition of anonymity, one contractor showed ABC News overdue invoices GFG Alliance is yet to pay, totalling more than $150,000.