A planned 24-hour strike on London Underground's Piccadilly Line has been called off, the RMT union has said.
But a walkout by drivers on the Central line will go ahead on Wednesday after last-ditch talks failed.
Tube workers had been set to stage a separate 24-hour strike on the Piccadilly line from 1.30pm.
The union said it was suspending the action after progress was made in talks in a dispute over industrial relations.
RMT general secretary Mick Cash said: "I want to pay tribute to RMT members on the Piccadilly line whose solidarity and resilience has been the decisive factor in forcing London Underground back to the negotiating table, where sufficient progress has been made to allow the scheduled action tomorrow to be suspended.
“The union remains vigilant to any attacks and abuse of policies, procedures and agreements on London Underground and will always take the required action to protect dignity, fairness and justice in the workplace.”
On the Central line, however, RMT blasted Underground bosses over "a comprehensive breakdown in industrial relations, a failure to employ enough drivers, a wholesale abuse of agreed procedures and the victimisation of a trade union member".
Mr Cash said these factors "tipped the situation over the edge", leading to Wednesday's strike action.
"The union is angry and frustrated," he said, "that the management side have squandered a golden opportunity to resolve the issues at the heart of the dispute through the talks process. As a result, the action goes ahead as planned.
"There is a growing culture on London Underground that revolves around refusing to employ enough drivers, bullying staff and expecting our members to pick up the pieces when the service breaks down."
Members of the drivers' union Aslef will also strike on Wednesday on the Central line, the second busiest on the network, as well as the Waterloo and City line.
Nigel Holness, managing director of London Underground, had previously called on the unions to call off all the "unnecessary" strike action.
He said: "The strike action called by both RMT and Aslef this week is totally unjustifiable.
"Both are demanding the reinstatement of drivers sacked over serious safety breaches - one who deliberately opened the doors of a train in a tunnel, and one who failed a drugs test."
Transport for London (TfL) said it would provide an additional 150 buses on Wednesday to help Londoners navigate the capital during the Tube strikes.
