Instructions: In this task, you are given an article. Your task is to summarize the article in a sentence.
Input: The move follows talks over the imposition of new rosters and a "breakdown in industrial relations".
Parent rail firm Govia Thameslink (GTR) is already in dispute with the RMT union over the role of guards on the Southern network.
GTR said it was a cynical and desperate attempt to heap misery on passengers.
The rail operator is currently running a reduced timetable to deal with ongoing disruption which it has blamed on crew shortages. The Aslef dispute is over the new timetable.
In a statement, Aslef said: "Ongoing issues in respect of discussions regarding the GTR's imposition of new rosters to facilitate the introduction of an emergency timetable remain unresolved.
"Aslef's executive committee consider that this amounts to a breakdown in industrial relations."
It said members would be balloted for strike action and action short of a strike with the ballot to close on 31 August.
But GTR passenger service director Angie Doll said: "Aslef members have been successfully operating this timetable for three weeks to deliver more reliable services for passengers and staff in the face of train crew shortages.
"To call a strike ballot against this timetable now is a cynical and desperate attempt to heap even more misery on passengers especially as we have met with Aslef on two occasions and have a further meeting with them next week on this specific issue."
The RMT is due to strike for five days from 8 August. Southern has said a "strike timetable" providing 60% of its normal services will be put in place if the action is not called off by Thursday afternoon, which is when two days of talks at Acas between the RMT and GTR are due to conclude.
That dispute is over new trains where the driver operates the doors using CCTV instead of guards, but the RMT has safety concerns and fears job losses.
In June, Aslef dropped legal action against the new trains and was also barred by the High Court from inducing GTR drivers to take industrial action.
Ms Doll said: "Twice Aslef has tried to block our plans to improve the railway and twice the courts have ruled their attempts unlawful."
A third union, the Transport Salaried Staffs Association (TSSA), is balloting more than 250 station staff in a row over ticket office closures.
TSSA leader Manuel Cortes has said that ballot will start on 10 August and any action in September will be co-ordinated with "our sister rail unions to maximise the impact".
Commuters have staged protests in London and the South East over continued disruption on the Southern rail network.
In a separate development, commuters in Sussex and Surrey are also facing disruption by bus drivers and engineers in a row about alleged bullying.
The Unite union said 71.4% of its members at Brighton and Hove buses and Metrobus in Crawley have voted to walk out. The bus company said both sides were in talks to find a resolution.
Output:
Train drivers employed by Southern Railway and Gatwick Express are to be balloted for strikes, the union Aslef has said.