Members of the Communications Electrical Plumbing Union (CEPU) are set to walk off the job on Tuesday, March 12.
The union said in a statement earlier this week that it had advised its members to take protected industrial action and instituted a ban on "specific duties during unpaid time".
However, the union said the telco informed it that a day's pay would be docked from workers every time they undertook such action.
"In effect, Telstra has threatened to lock employees out of their employment -- basically saying: 'Engage in this ban and you might as well stay home, because we won't pay you anything'," the union said.
"By doing so, Telstra has displayed utter contempt for you and your rights to fight for what you deserve, along with disgraceful contempt for their customers who will now, instead, be significantly affected by an escalation in action."
Consequently, all union members covered by the enterprise agreement with Telstra have been directed to strike on March 12, unless they work in Triple Zero centres or do emergency and medical work.
The union is warning its members to ignore all notices from Telstra management, particularly on whether to be involved in the strike, and is telling members that they do not have to inform management of their intentions.
"Like all employers, under the Fair Work laws, Telstra isn't obliged to accept an employee only performing part of their job," a Telstra spokesperson said.
"For one of the three types of industrial action notified by the CEPU last week, we advised employees that we are not accepting work associated with that industrial action. This meant they would not be required at work that day if they chose to take that action.
"The CEPU has since retracted its notice of action and advised that it will organise strike action for one day next week. Under Fair Work laws, we are not permitted to pay people who are engaging in strike action."
After putting industrial action to a vote in February, 88 percent of union members who voted were in favour of action.
Telstra said last month that customers should expect business as usual if action were to occur, with the company having contingency plans to ensure operations continue.
"Our focus will be on ensuring that our customers and the vast majority of our people who are not participating in any action are not affected by any CEPU action," Telstra group executive of transformation and people Alex Badenoch wrote.
Badenoch said CEPU members are around 10 percent of Telstra's employee base, and only 56 percent of members voted. The Telstra HR honcho pointed to the telco's Telstra2022 strategy as a response to competitive pressures, and said the deal put forward by the company was fair.
"It is a mixture of fixed pay and incentive pay based on the performance of our business and people," Badenoch said.
"Over many years, we have consistently paid increases under our [enterprise agreement] that exceed that of our main competitors and continue to offer industry-leading terms and conditions in areas like hours of work, leave benefits and redundancy protections. However, we need to act with restraint at this challenging time."
A Telstra spokesperson on Wednesday reiterated that the telco has plans in plans to avoid disruption, and the company was committed to "constructive discussions with our people and unions to reach a new agreement".
The union has long complained that the offers made by Telstra are a cut in real wages.
"At a time where Telstra is sacking 9500 of your colleagues and executives are still taking home exorbitant pay packages – a pay cut, in real terms, for those who remain is simply unacceptable," the union said last month.
"You deserve a new EBA with a fair pay rise that allows you and your families to keep up with the rising cost of living and reaching such an agreement, with minimal impact to you and your pay packet, is always going to be your Union leadership's priority."
Earlier this month in its first half results, Telstra posted a AU$223 million drop in revenue to AU$12.6 billion, and earnings before interest, tax, depreciation, and amortisation also dropped by 16 percent, from AU$5.1 billion to AU$4.3 billion year on year.
Restructuring costs reached AU$0.3 billion for the six months to December 31.
Updated at 4.49pm AEDT, March 6, 2019: Added comment from Telstra.