PERU drug mules Michaella Connolly and Melissa Reid will be in jail for Christmas.
It follows a decision by court workers to go on strike over low wages.
The pair had hoped an early plea to drug smuggling charges could let them home to serve out their jail sentences in UK prisons.
The 20-year-olds had pleaded guilty to smuggling £1.5million of cocaine through Lima’s Jorge Chavez airport in August to get a sentence of six years and eight months – low enough to apply to serve it in Britain.
Michaella, of Dungannon, Co Tyrone, and Melissa, from Glasgow, now face months crammed in tough Virgen de Fatima jail as the courts deal with a backlog.
The strike by court staff started as a day of action but has not led to an indefinite stand off.
Union leader Jorge Cotrina said: “The reasons for the strike is that we, the judicial workers, do not feel represented and we feel neglected by the head of our courts Dr San Martin since the man knows the low salaries that we have.
“It does not even each a tenth of what he earns.
“He has engaged in a struggle by demanding improvements only for magistrates so he makes this look like this is only a problem for the magistrates and we really feel upset and this is why we have demanded social inclusion and salary increases start with us because we are thrones who have the lowest salaries.
“This is why we are striking.”
Prosecutors don’t believe the girls’ stories that they were forced to take the drug consignment at gunpoint.
They believe they were willing participants in the drug smuggling operation to bring the drugs back to Spain and then onto the UK, including in Northern Ireland.