Strike-hit rail operator Southern has lodged a legal appeal in a bid to prevent further industrial action.
On Thursday, Southern's parent company Govia Thameslink (GTR) failed at the High Court to ban Aslef, the drivers' union, from staging walkouts.
GTR has now lodged an appeal against the High Court decision.
The company has already been hit by a series of strikes by the RMT union in a long-running dispute over guards' roles.
The latest action came this week with three days of strikes by the RMT - action that coincided with an overtime ban by Aslef.
Services continued to be affected on Friday after the strike ended at midnight.
Southern has warned any further walkouts by drivers will lead to no services on most routes.
'Don't attempt to travel'
On Friday, GTR chief executive Charles Horton said: "This industrial action is having a severe and significant impact on our ability to run our train services and causing massive disruption to the 500,000 passengers who travel with us every day.
"We were granted permission yesterday by the judge to make an urgent appeal and we have a duty to our passengers to do all we can to prevent the wholly unjustified industrial action continuing.
"Our passengers have suffered months of travel misery and we call again on the unions to call off their action and work with us to find a resolution to their dispute."
No date has yet been set for the Court of Appeal hearing.
Southern has warned there will be no service on 13, 14 and 16 December when both Aslef and the RMT go on strike.
An alert to passengers on its website said: "You should not attempt to travel."
Aslef, which described Thursday's court ruling as a victory, said GTR's legal action was a waste of "shareholders' money, passengers' money and taxpayers' money".
Southern had argued the consequences of the strike were a breach of its customers' rights to travel under EU law.
London Mayor Sadiq Khan has called on unions to end the dispute with Southern, but also criticised the government for "washing their hands of the crisis and abandoning passengers in the process".
He said: "The ongoing chaos on Southern rail services is a total disgrace that is badly failing commuters who just want to get to work and back."
A spokesman for the Department for Transport said: "Passengers are once again facing misery because of this needless and unjustified action.
"The union leaders have continually rejected a deal that means no job cuts and ensures that on-board supervisors will carry on delivering safe, accessible and more reliable rail services.
"We call on RMT to put passengers first and stop this damaging action."
The RMT is fighting changes to the way services are operated, including giving drivers responsibility for opening and closing doors, amid fears over safety and job cuts.
Throughout the latest action, RMT chief Mick Cash has called for further talks and said members remained "rock-solid and absolutely determined in their action in defence of rail safety".
Aslef's first full walkout is expected to begin at 00:01 GMT on Tuesday and last for 48 hours.
The RMT union, which has been staging strikes since the summer, is also planning further stoppages either side of Christmas.
Southern planned rail strike dates:
00:01: Tuesday 13 December to 23:59 Wednesday 14 December (Aslef)
00:01 Friday 16 December to 23:59: Friday 16 December (Aslef)
00:01 Monday 19 December to 23:59 Tuesday 20 December (RMT)
00:01 Saturday 31 December to 23:59 Monday 2 January (RMT)
00:01 Monday 9 January to 23:59: Saturday 14 January (Aslef)