At its national conference next month, the Civil and Public Service Union will debate a motion to ballot 13,000 public sector workers for industrial action if there are any attempts to deduct the charge from their salaries.
Executive member of the union Terry Kelleher said a motion has been passed calling for the tax to be scrapped.
However, the union leadership has not taken an official position on the charge and has not called on its members to boycott it.
Meanwhile, the Unite trade union has urged its 50,000 members not to pay the charge, which it described as “one more punch below the waist”.
The union said it was not opposed to a property tax if it was “fair” to everyone but did not agree with a flat charge being imposed “without care or thought” on every household.
Unite promised to “stand beside” members who are willing to show courage and resist the charge.
But asked of they would help members if they are fined for non-payment, spokesperson Rob Hartnett said: “We’re a long way from determining what measures that support might entail. As it stands at the moment we are a long way from the household charge being implemented.”
Ten days ahead of the Mar 31 deadline, 279,980 of the 1.6m eligible property owners have signed up for the charge, according to the Department of the Environment.
A new system of payment through post offices, which came into effect yesterday, has so far failed to have a serious impact on registration numbers, with an additional 11,000 people signing up since the weekend.
If there is widespread avoidance of the payment, the Government can avail of a law that will allow a court to order for the deduction of a €100 fee from the pay or social welfare benefits of homeowners.
A late-payment fee of €10 will apply if the charge is not paid within six months of the due date, €20 between six and 12 months and €30 if the payment is 12 months late. After two years, the penalty rises to €280 with the combination of charges, late-payment fees and interest.
Local authorities will also have the power to take prosecutions against homeowners who fail to pay, with fines ranging from between €1,000 and €2,000.
The fines, as well as late payments, could be taken from wages or welfare payments under changes to the Fines Act to go through the Dáil this year.
The department said there are no plans to extend the deadline beyond this month, which Fianna Fáil said was “no longer tenable”.
The party’s environment spokesman Niall Collins said Environment Minister Phil Hogan should “put his hands up and admit that this has not been executed in the right way”.