In a 10-minute speech to about 100 employees at the Philadelphia Regional Financial Center, Cheney called the checks "a shot of energy at the right time and in the right way."

"This is the first day for mass production of those rebate checks under the Economic Stimulus Act of 2008 - and the largest number of those checks will be printed right here in Philadelphia," he said.

He went on to say that the rebates "will help strengthen the case for permanent tax relief. ... In the months to come, the American people will once again prove why our economy remains the envy of the world."

The Cheney visit tied up midday traffic between the center and the Willow Grove Naval Air Station.

The first rebates, paying up to $1,200 for some couples who filed taxes jointly for 2007, went out last week as direct deposits to bank accounts.

About 130 million payments will be made, including 88 million paper checks expected to be mailed by July 11.

The lower the last two digits of a taxpayer's social security number, the earlier a taxpayer is assured of getting a check, according to the IRS website, www.irs.gov.

For example, if a taxpayer's social-security number ends in 50, and the person set up direct deposit, the payment "will be transmitted no later than" tomorrow, May 9, according to an IRS chart.

If the same person's payment is to be sent by check, it should "will be mailed no later than" June 13.

To see the schedule, click this link: http://www.irs.gov/irs/article/0,,id=180250,00.html.

The other centers are in San Francisco; Austin, Texas; and Kansas City, which Treasury Secretary Henry Paulson visited today.

The four centers print checks for all sorts of federal payments, including social-security benefits, federal pensions, income-tax refunds, veterans' benefits, salaries and payments to vendors.

The Associated Press contributed to this report.