By Ana Isabel Martinez

MEXICO CITY, June 17 (Reuters) - The Mexican association that groups major global oil services companies warned that it is going through an "unprecedented crisis" due to the lack of payments from the state-owned oil company Pemex, the world's most indebted energy company.

In a letter sent to President Claudia Sheinbaum and released on Monday afternoon, the association warned that many of these companies may have to stop operations as early as July. The letter did not specify the amounts owned to the group's members, which include Baker Hughes BKR.O, Halliburton HAL.N, Weatherford WFRD.O, SLB Oil & Gas SLB.N and Grupo Mexico GMEXICOB.MX.

Pemex, one of Mexico's largest companies, has an outstanding debt with an extensive list of suppliers and contractors of around $20 billion, in addition to another financial debt of $101 billion, despite the injection of billions of dollars from the government in the last few years to face the amortizations.

In the letter, the Mexican Association of Oil Services Companies (AMESPAC) urged Pemex to process and release the invoicing for services rendered in 2024, to guarantee regular invoicing and timely payment for those of 2025, and to design a payment plan to settle all historical debts owed to companies of the sector.

The service sector has significantly decreased its activities because of the lack of payments from Pemex, AMESPAC said in the letter, adding that "its cash flow is seriously compromised and in most cases it cannot guarantee operational continuity as of July of this year."

"We expect a precise response that addresses our concerns and reverses the deterioration of national hydrocarbon production, which compromises Mexico's energy security and sovereignty," the letter concluded.

This is not the first time that AMESPAC has called on the government and Pemex to urge payments and their impact on the state-owned company's hydrocarbon production.

Last week , Reuters exclusively reported that Hokchi Energy, one of Mexico's largest private oil producers, has sought new ways to market its hydrocarbons in the face of delays in payments by Pemex.

Despite numerous promises of payments and partial settlements, liabilities continue to accumulate while oil production continues to fall. Pemex reported an 11% year-on-year plummet in production during the first quarter, in addition to posting losses.

(Reporting by Ana Isabel Martinez; Editing by Aida Pelaez-Fernandez and Marguerita Choy)

((natalia.siniawski@thomsonreuters.com;))