Tube bosses launched a legal challenge on Wednesday, saying the ballot for strike action by one of the unions was "invalid".
The RMT and the train drivers' union Aslef had voted for three one-day strikes on consecutive Mondays over safety and job security, to start from next week.
Wednesday's High Court ruling is expected to prevent the first strike planned for Monday and could force a re-run of the ballot.
The judge ruled there had been "non-compliance" by the union with statutory provisions relating to giving notice of industrial action.
He will give reasons for the injunction on Thursday and rule on whether the strike ballot must be held again.
Earlier, Mr Jeffrey Burke QC, for London Underground, told the judge the Rail, Maritime and Transport (RMT) union failed to supply information about the number, category and workplace of the estimated 6,000 employees concerned.
'Mass disruption'
He said: "The purpose of the requirement is to help the employer make plans so as to avoid or reduce the impact of the proposed industrial action."
He said the planned strike would disrupt the journeys of three million passengers who use the tube each day with a loss of £3m in revenue.
Talks aimed at resolving the row had ended without agreement on Tuesday.
London Underground had earlier issued a statement which read: "Most staff have not voted to strike and our customers certainly don't want it. That is why we are taking legal action."
Part-privatisation fears
The RMT had said it was "astonished" by LU's legal move.
Assistant secretary Bob Crow said the union would await the judge's full ruling on Thursday before making any comment on whether the strike scheduled for Monday would be called off or whether the union would launch an appeal.
Speaking after the ruling an LU spokeswoman said: "We are saddened that we have had to come to court.
"We still have talks with the unions tomorrow and we are still hoping that we can resolve this dispute so we can provide a full service for our three million daily passengers."
London Underground managers met members of the Health and Safety Executive in December after fears were raised about the government's plans to part-privatise the Tube.
Deputy Prime Minister John Prescott, who called the meeting, said then that the part-privatisation would not go ahead if there were safety fears due to the break-up of London Underground into separate organisations.