WASHINGTON —  An effort to increase the minimum wage in all states, even those that already have wage floors higher than the federal base, failed Thursday after Democrats labeled it a "poison pill."

Democrats said the Republican proposal was designed to kill underlying minimum wage legislation.

An amendment offered by Sen. Jim DeMint, R-S.C., was an effort to show how raising the federal minimum wage from $5.15 to $7.25 over 26 months would have no effect in eight states because they already have wage floors of $7.25 or higher. Another two states have scheduled minimum wage increases that also would place them above the proposed federal floor.

Eighteen other states have higher minimum wages than the current federal floor, but not as high as the $7.25 in the proposed legislation.

"This is a mandate on low-cost-of-living states, but not on high-cost-of-living states," DeMint said.

The amendment failed on a 78-16 vote after Sen. Edward Kennedy, D-Mass., raised a budget point of order challenging it. Massachusetts is among the states that already have a higher minimum wage and would not be affected by the federal law.

Kennedy called the amendment a ploy "intended to give senators in high minimum wage states an uncomfortable vote today not to raise wages for hardworking Americans."

States that already have higher minimum wages than the federal floor tend to be clustered in the Northeast and the Pacific Coast. States without their own wage floor are in the Midwest and the South.