Some 300 of the company's bus drivers in Preston and Chorley are going on strike on Saturday, May 11 after pay talks broke down with the firm.
Regional industrial organiser at Unite the Union, John Boughton, confirmed that a series of one day strikes are to commence.
Following tomorrow there are planned strikes on Tuesday May 14, Saturday May 25, Tuesday May 28, Friday May 31 and Saturday June 1.
Subsequently St Michael’s CE High School in Chorley has warned parents and carers to organise 'contingency plans' for students who have GCSE exams on strike days, warning that "exams will start at 9am whether candidates are missing or not".
In an email to parents and carers, a school spokesman said: "We have been made aware that there will be proposed industrial action on Stagecoach buses, they may run a reduced or cancelled timetable.
"Exams start next week, pupils and parents/carers should ensure they have a contingency plan if buses are cancelled/reduced.
"Exams will start at 9am whether candidates are missing or not."
Other schools in the town are also set to speak to parents about the situation and how the strikes may affect students.
Steve Mitchell, headteacher at Parklands Academy, said: "We use Tyrers for our school buses, so in theory our students should not be affected.
"We will communicate with our parents tonight (Friday, May 10) via our parent bulletin about the Stagecoach strikes, though."
Earlier this week Stagecoach said it was drafting in extra drivers to help minimise disruption, with bosses saying they were “disappointed” over the industrial action.
Regarding potential GCSE exam disruption, a Stagecoach spokesman said: "We are working closely with our travel partners to ensure minimum disruption is caused during planned strike action.
"Most routes will run on a reduced service with extra staff drafted in to assist.
"Currently only one of the six planned strike days takes place during the school term.
"It is anticipated that the majority of routes serving local schools will see little or no change as a result of strike action.
"Unfortunately a small number of services will not be operating."
Stagecoach has advises customers wishing to travel with them to check their journey in advance.
Full details can be found at www.stagecoachbus.com/promos-and-offers/merseyside-and-south-lancashire/potential-strike-action or on Twitter at @StagecoachMCSL.
The company spokesman added: "We would like to reiterate our stance that our door is open if the union wants to have sensible and constructive discussions."