13 May, 2004, 20:31 GMT 21:31 UK

Michael's mother blames his autism on the MMR jab

Isabella Thomas, who has two sons with autism, complained to the Law Society about a letter warning of legal costs and inviting her to drop her claim.

Law firm, Lovells, acting for drug firm Merck said it was normal procedure.

The letter was sent to 500 parents who are asking for legal aid to be continued in their cases.

Lovells, lawyers for MMR manufacturer Merck, said the letter "was to inform claimants about the position in relation to costs and to make an offer which would help those who wanted to know where they stood in relation to the litigation".

The spokesman said: "It is quite normal for defendants' solicitors to write such letters."

But Mrs Thomas, 47, said the solicitors' letter was a "threatening" letter to "vulnerable parents" asking them to "sign away their children's lives".

They picked on the wrong ones when they picked on mothers   Isabella Thomas

She claims her 12-year-old son Michael and his 10-year-old brother Terry were both damaged by the jab.

"It is bullying - they're trying to frighten us into backing down," she said.

She said agreeing to the letter would mean never being able to sue the drug company even if scientists later proved a link between the vaccine and autism.

She said the letter gives until Friday to decide whether to waive rights to compensation, or fight on and be liable for costs.

In February, the Legal Services Commission wrote to parents asking them, on grounds that their action had little prospect of success, to make their case for legal aid to continue.

Mrs Thomas said that most parents were planning to fight for legal aid and continue with action against Merck.

"They picked on the wrong ones when they picked on mothers," she said.