The union, which represents almost 2,500 workers in Northern Ireland, balloted members currently in dispute over pay.
Workers at the EirGrid owned company have not received an annual pay award since 2015. Staff overwhelmingly rejected previous offers by the company.
More than 100 workers were asked if they supported strike action, and action short of strike. 90% of respondents voted to support it.
Action is likely to start in April unless there is a breakthrough in negotiations. Angela Moffatt, Prospect’s negotiator who represents the workers said: “SONI has failed to make a meaningful offer to members to date – offers have been derisory.
“SONI has been awarded monies by the utility regulator to pay RPI increases annually to staff. It has admitted it is under budget on salaries and has been in profit during the period.
“There is no excuse for the current situation. SONI’s behaviour in prolonging the dispute is reckless and cavalier.
“Unless the company changes tack and fast, we are heading into a prolonged period of industrial action. This will have negative impacts on Northern Ireland at the worst possible moment.
“We have taken steps to ensure any action does not harm the safety of the public but we are still concerned about the disruptive impact of any action.
“We are willing to continue to negotiate but we need a more realistic approach from SONI.
They can no longer be led by the nose by poor EirGrid strategy on pay and industrial relations matters. They need to wake up, take back control and start treating their staff with respect and fairness.”
The union will continue to seek resolution to avoid industrial action, but Prospect is warning of major impacts on third party organisations if the strike goes ahead.