Kent County Council (KCC) is expected to put up its Young Persons' Travel Pass from £200 to £250 in September - a year after the price doubled from £100.
"We have just set up an e-petition and we will be emailing all the schools and hoping people will sign," said Staplehurst campaigner Katya Thornton.
KCC said it could not provide a cheaper pass because of government cuts.
The travel pass gives unlimited access to Kent's buses for 11 to 16 year-olds on weekdays between 06:00 and 19:00 from the start of the academic year until 31 July.
"Some people will say the increase is only £50 but that's a 25% rise and its coming on top of last year's rise," said Ms Thornton.
"For some people like me this has a real impact.
"It's very unfair for those of us who live in rural communities because I don't have the right kinds of schools on the doorstep.
"I would prefer to send my children to a school five of 10 minutes away where they could walk but I can't do that."
Leader of the UKIP opposition on the council Roger Latchford, said he was appalled at the increase and would oppose it when it was debated by the council's cabinet on Monday.
Tory-run KCC said buying a bus card directly from the operator could cost more than £800 a year.
It said government cuts meant the council had to save £209m over the next three years and subsidising bus passes currently cost the council about £15m a year.
"It is a discretionary scheme - we don't have to do it," said Conservative Matthew Balfour.
"Our subsidy is being reduced but that still leaves a cost to the taxpayer of £338 per pass."
Parents have vowed to fight a £50 increase in the cost of bus passes for Kent secondary school students.