A father who won a High Court battle over taking his daughter on holiday during term time has set up a company to help parents in the same position.
Jon Platt said since his case had been in the spotlight he had been contacted by "hundreds" of parents who believed they had been wrongly fined.
School Fines Refunds Limited's sole purpose will be to help parents recover money where they have been unlawfully fined.
Mr Platt told BBC Radio 4 programme You & Yours: "Parents are contacting me in their hundreds about this.
"Local authorities are fining people based upon a single day - or two days, or sometimes five days - of unauthorised absence when they had no reasonable grounds to believe that a criminal offence had been committed.
"And hundreds of thousands of parents have paid millions of pounds in fines when they did absolutely nothing wrong.
"The only reason they paid them was the fear of the consequences of going to magistrates' court."
He warned that if local authorities do not comb through their records of penalty fines and "do the right thing", his new company is prepared to take on thousands of claims.
Mr Platt successfully won his case against Isle of Wight Council when they tried to charge him £120 for taking his youngest daughter on an eight-day trip to Florida.
The ruling means children who attend school regularly can now go on holiday during term-time without being fined.
The term "regular attendance" has still not been defined but in Mr Platt's case his daughter had more than a 90% attendance record.