WASHINGTON — The Obama administration is threatening to veto a measure being considered by House Republicans that would ban almost all abortions after a fetus reaches the age of 20 weeks.

The legislation expected to pass the Republican-controlled House as early as Tuesday has no chance of becoming law in the near future since the Democratic-led Senate will ignore it. But the measure gives social conservatives a rare chance to promote their anti-abortion agenda and lays the groundwork for what could be a future challenge to the 1973 Supreme Court decision that confirmed a woman's right to late-term abortions.

In issuing the veto threat, the White House on Monday said the measure "would unacceptably restrict women's health and reproductive rights and is an assault on a woman's right to choose."