The judge suggested Arwyn Thomas was sacked for his union activities Tube workers are to go on strike from 2100 BST in protest at the sacking of a driver.
The Rail, Maritime and Transport union (RMT) alleges Arwyn Thomas was sacked for his union activities and demands his reinstatement.
London Underground (LU) said it will abide by a tribunal ruling due shortly and the strike will “achieve nothing”.
The strike is due to last six hours, but LU claims it will cause little disruption.
LU managing director Mike Brown said: “This strike action will achieve nothing and I urge the RMT leadership to calmly await the outcome of the employment tribunal without any further strikes.
“I have given a cast-iron assurance that if the tribunal rules that we should re-instate or re-engage Arwyn Thomas, then we will do so.
“We have given that assurance in writing before this strike action and I make it again now, so there can be no justification whatsoever for the RMT to continue to threaten Londoners with strike action.”
At an interim hearing a judge suggested a tribunal was “likely” to find Mr Thomas was dismissed for his union activities.
Further planned strikes could affect people travelling to the Wimbledon tennis championships.
An RMT spokesman said: “Unfortunately, management refused point blank to even discuss re-employing Arwyn.
“Therefore, we have no option but to go ahead with our strike action to defend our longstanding rep and activist.”
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