BOSTON (AP) — Massachusetts Democrats hope a planned vote in the U.S. Senate will draw a bright line between Republican U.S. Sen. Scott Brown and his chief Democratic rival Elizabeth Warren on taxes.

Brown is also hoping for the same bright line.

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The Senate is planning to vote on President Barack Obama’s call to raise taxes on millionaires — also known as the Buffett rule after billionaire investor Warren Buffett, who says he pays a lower tax rate than his secretary.

Warren supports the bill, which she said would ensure that millionaires and billionaires pay their fair share in taxes.

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Brown said he opposes the rule, arguing that raising taxes on any group in a fragile economy is a bad idea.

The vote could happen as soon as Monday.

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