H&R Block Inc said on Wednesday its Block Financial Corp. unit tapped working capital credit lines twice as a skittish market cuts off its access to short-term debt financing.

Block said it drew down $200 million from working capital credit lines on Aug. 16, which was then repaid with a second draw of $850 million on Monday. H&R Block has $2 billion available in committed, revolving working capital lines that mature in 2010.

The credit markets have become increasingly constrained and unstable, Block Chief Financial Officer William Trubeck said in a statement. We have decided to substitute this more stable source of funds to support our short-term needs.

Shares of H&R Block fell 24 cents, or 1.2 percent, to $19.55 in early trade on the New York Stock Exchange.

The largest U.S. income tax preparation company said Block Financial, which provides funding for H&R Block's various businesses, will continue tapping working capital lines until commercial paper markets stabilize and debt-pricing returns to normal.

Moody's on Tuesday downgraded Block Financial debt to Baa1, from A3, citing its concern that continued turmoil in the U.S. mortgage markets might jeopardize H&R Block's pending sale of its Option One Mortgage subprime unit to Cerberus Capital Management.

A buyer's strike crippled most of the market for U.S. asset-backed commercial paper, or ABCP, Tuesday. Most companies are still finding short-term cash by issuing traditional commercial paper -- debt that on average matures in 30 days but can extend for as long as 270 days.

The rates that investors are demanding for ABCP jumped on Tuesday to 6.05 percent from 5.90 percent for paper maturing in one month. That rise occurred despite efforts by the U.S. Federal Reserve to ease global credit fears by cutting its discount rate, charged on direct Fed loans to banks.

(Reporting by Joseph Giannone)