There are a handful of issues in U.S. politics -gun control, abortion and gay marriage foremost among them -guaranteed to send partisans scrambling to their battle stations.

Now add another one to that list: breastfeeding.

An effort by Michelle Obama to promote breastfeeding as a way to prevent childhood obesity is being denounced by Republican lawmakers and right-wing pundits, who accuse the U.S. first lady of seeking to impose the nanny state on American motherhood.

The conservatives' ire has been further fuelled by an Internal Revenue Service decision this month to allow mothers to deduct the cost of breast pumps from their taxes as medical equipment.

"I've given birth to five babies and I breastfed every single one," Rep. Michele Bachmann, a Minnesota Republican, told radio host Laura Ingraham this week.

"To think that government has to go out and buy my breast pump, that's the new definition of a nanny state."

Bachmann, who chairs the Tea Party caucus in Congress and is weighing a presidential bid, suggested the first lady was behind the IRS decision and may even be seeking to mandate breastfeeding.

Michelle Malkin, a conservative blogger, said the IRS decision favours "breast-pumping working mothers" at the expense of stay-at-home nursing mothers.

"We don't need Big Brother or Big Mother to lead the Charge of the Big Bosom to persuade us of the personal benefits," Malkin wrote.

The White House says the first lady plans to tread carefully on the issue, and isn't trying to impose breastfeeding on anyone.

On the website Politics Daily, a spokeswoman for Obama told journalist Lynn Sweet the first lady is sensitive that the decision to breastfeed or bottle-feed is a "very personal choice," and that she is only hoping to make it easier for those who opt to nurse.

The first lady recently said she would promote breastfeeding as part of her broader Let's Move campaign, which aims to reduce childhood obesity by promoting exercise and healthy eating habits.

"Kids who are breastfed longer have a lower tendency to be obese," Obama said.

Several studies have linked breastfeeding to a lower incidence of child obesity, and the Centers for Disease Control says an analysis of the science shows "initiation of breastfeeding resulted in a significant overall reduced risk of overweight" children. The CDC also says protection against becoming overweight from being breastfed "may persist into the teenage years and adulthood."

Breastfeeding advocates in the U.S. say they're disappointed in the controversy and are applauding the first lady "for taking a stand" on the issue.

"I think it is unfortunate that we politicize something so important as our children's health," said Trish MacEnroe, executive director of Baby Friendly USA, a not-for-profit group that works with hospitals to help promote breastfeeding among new mothers.