General Motors Corp. (GMGMQ) Chief Executive Fritz Henderson said auto parts makers face a "draconian" revenue drain if bankruptcy court fails to approve a sale of GM's assets to a new company next month.

Henderson, in an affidavit filed Thursday, said GM plants shuttered during much of the summer may not reopen if the sale is blocked.

With many auto suppliers either on the brink of bankruptcy or already in protection, Henderson said a longer shutdown at GM could deal a final blow to struggling companies.

"Many suppliers are already in the midst of a severe liquidity crisis, which has only been exacerbated by the current shutdown of GM production facilities," he said.

"Without prompt approval of the 363 transaction and the renewal and ramp-up in production by New GM, the effect on certain suppliers will be fatal."

Already this year, 13 major auto parts suppliers and two indirect suppliers have filed for Chapter 11 protection, according to the Original Equipment Suppliers Association.

Lear Corp. (LEA), a maker of seats and auto electronics, is working to fashion a pre-packaged bankruptcy deal and could file for Chapter 11 as early as next week, according to people familiar with its plan.

Troubles have been mounting for years in the supplier industry, which accounts for more than three-quarters of employment in the U.S. auto sector.

Suppliers have struggled to adjust to the precipitous fall in global auto demand, exacerbated by the shutdown of plants by GM and Chrysler LLC.

Chrysler, which emerged from bankruptcy earlier this month, shut down all of its U.S. factories for almost two months.

GM's bankruptcy plan separates the company's more attractive operations from "bad" assets; the latter will be wound down or sold in a lengthy liquidation. The "new GM" assets would be transferred to an entity owned by the U.S. and Canadian governments, a health care trust for members of the United Auto Workers union and the company's unsecured creditors.

Henderson said in the affidavit that virtually all of the company's dealers have agreed to either stay in business with the company or accept offers to wind down their business.

GM wants to trim about 1,900 of its 6,000 outlets. Around 4,100 dealers received offers to stay with GM, and 99.6% have agreed, he said. Among those earmarked for closure, GM reversed its decision in 64 cases. Some 98.8% of those given wind-down offers have accepted them, he said.

-By Sharon Terlep; 248-204-5532; sharon.terlep@dowjones.com.