Feminists in the United States, "fed up" with election-year attempts to erode their hard-won gains, issued a sharp reminder that women make up a voting bloc that cannot be ignored.

HERvotes, a coalition of 51 women's groups, vowed to ensure that several decades of progress in health care, education and labor rights will not fall by the wayside in the run-up to the November general election.

"Women are outraged with the constant politicization of theses issues with no regard for half of the population," said Eleanor Smeal, president of the Feminist Majority Foundation.

"The gender gap is alive and well," agreed Lisa Maatz, chief lobbyist for the American Association of University Women, who added: "We are mad and we are fed up."

In a campaign year in which the economy and jobs were the initial dominant themes, social conservatives have thrust birth control and abortion to the top to the agenda at the state and federal level.

On Thursday, the Senate rejected a proposal by Republican senator Roy Blunt to exempt employers who object to birth control measures from having to abide by health insurance rules set out by President Barack Obama.

In the name of conscience and religious freedom, Roman Catholic bishops last month opposed health insurance coverage for contraception -- forcing Obama to come up with a compromise that failed to resolve the issue.

On Tuesday, Virginia state senators approved a bill requiring abdominal ultrasounds for women seeking an abortion, while Pennsylvania is considering legislation that would oblige doctors who advise on abortions to systematically use the term "unborn child."

In Oklahoma, doctors could be required to make women undergoing an abortion to first listen to the heartbeat of the fetus, according to a proposal that was put to a vote on Monday.

Terry O'Neill, president of the National Organization of Women, which is part of the HERvotes coalition, said that, taken together, such legislation was intended "to humiliate women."

By HERvotes' calculations, more than 1,000 pieces of draft legislation were presented in 2011 -- and 163 adopted -- to limit the right to abortion or contraception.

"Today, the only way or the best way to really speak out is to vote," said Maatz, whose group is campaigning in 15 key states "to make sure to bring women's voices into the discussion."

Blogs, Twitter, campaign videos and protests outside legislatures are among the tactics that women's groups plan to use to put across the point that by targeting women's issues, candidates "are losing votes," O'Neill said.

"Not only is it extreme and ridiculous, but it's also not very smart," said Maatz, adding that social conservative Rick Santorum lost the Republican primary in Michigan to Mitt Romney this week because women, especially young women, did not vote for him.

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