Washington ? The U.S. Treasury is set to begin mailing tax refunds of up to $400 per child to 25 million families later this week — a cornerstone of President Bush’s effort to juice the economy, but a benefit that has sparked controversy.

Bush will trumpet the imminent arrival of the refunds Thursday, when he and Treasury Secretary John Snow visit a Philadelphia office where the checks are being printed.

But Democrats and their allies on Wednesday continued their effort to spotlight the 6.5 million low-income families who will not receive the money.

To protest lack of action on a bill to extend the relief to the working poor, the Democrats slowed action in the House for hours by forcing back-to-back roll call votes on routine matters.

The child credit rebate checks mailed Friday will go to about 8.6 million taxpayers whose Social Security numbers end in 00-33. Two more rounds of checks will be mailed on Aug. 1 and Aug. 8.