Members of the RMT union were already due to take strike action over the long-running dispute, and extra dates have now been added.
It comes after talks to resolve a row over driver-only trains broke up.
The planned dates are: Sunday 3 July, Sunday 10 July, Monday 11 July, Thursday 14 July, Saturday 16 July and Sunday 17 July.
The dispute concerns driver-only-operation trains, where the driver is asked to close the doors at stations, instead of the on-board conductor.
Unions insist the procedure poses a risk to passenger safety but ScotRail has said it would always schedule a second person on trains.
RMT general secretary Mick Cash said: “Our members on ScotRail stand determined and united in this fight for jobs and safety on Scotland’s rail services.”
He said union members had “no choice” but to move to a new phase of industrial action.
ScotRail’s managing director Phil Verster said he would hold fresh talks with union leaders but his offer was dismissed by the RMT as “classic divide and rule”.
Mr Verster said: “The RMT have announced another round of needless, damaging strikes on the evening before we are due to come together for talks.
“This clearly marks the difference between our two approaches. We want to talk, they want to strike.
“ It is important to remember that this is a strike about who opens and closes doors on our trains. No-one will lose their jobs, no one will see their pay drop or see any change to their terms and conditions.”
Scotrail said it is running around 70 per cent of services on strike days.
It also emphasised how 59 per cent of its customers already travel on a train where the doors are opened and closed by the driver
RMT members have already staged four walkouts.
Routes hit by the stike action include Edinburgh to Aberdeen, Glasgow Central to Edinburgh, Aberdeen to Inverness and Glasgow Queen Street to Oban. A number of other routes are cancelled or reduced. Replacement bus services will operate some of the routes.