Court staff have rejected plans to introduce a "divisive" pay system which union leaders said would lead to workers earning different amounts of money across England and Wales.
The Public and Commercial Services union (PCS) said the "postcode" pay offer would lead to some workers having a wages cut.
More than 6,000 union members voted against the proposed deal, with just 244 in favour, a majority of 96%.
The courts staff will be among 270,000 civil servants taking part in a one-day national strike next Tuesday in a row over jobs, pay and privatisation.
PCS general secretary Mark Serwotka said: "The overwhelming vote rejecting postcode pay illustrates the growing anger amongst courts staff, who will be taking part in a one-day stoppage on May 1 in a civil service-wide dispute over below-inflation pay, job cuts and privatisation.
"Job cuts, compounded by below-inflation pay, is a massive problem not only in the courts service but the civil service as a whole. Any move to introduce postcode pay be it in the courts or elsewhere will be resisted."
