An increase of up to 70% in the price of formula milk for babies has provoked a consumer backlash, with parents accusing the company behind the move of trying to profit from "captive" consumers.

Heinz's replacement of its Farley's range with a more expensive brand called Nurture caused outrage and calls for temporary boycotts of all its products on website discussion threads as well as complaints to retailers.

The Guardian understands a bigger formula milk manufacturer is also planning to increase prices, while a third, which last raised them about six months ago, says it has no plans to do so for the foreseeable future.

Asda, which is selling Heinz Nurture at £7.98 for 900g, up from £4.68 for Farley's, said it had received hundreds of complaints from customers.

The NHS encourages mothers to breastfeed if possible. Its last big survey, in 2005, suggested 76% of mothers did so for at least six months, up from 69% in 2000. Half of all mothers continued breastfeeding after six months.

Figures from market analysts Taylor Nelson Sofres also suggest baby milk sales for under-twos are slipping in value and volume, although they are still worth more than £140m a year in the UK.

Tighter rules have recently been introduced over the promotion of formula milk, although new labelling regulations have been delayed following legal challenges.

Gail Johnston, educational and professional development adviser at the Royal College of Midwives, said mothers with concerns should talk to their health visitor before changing in case there were specific reasons for their babies being on a particular formula. "You may find baby is a bit more unsettled in the initial 24-48 hours after a change