By Foo Yun Chee and Supantha Mukherjee

BRUSSELS (Reuters) -A code of practice designed to help thousands of companies comply with the European Union's landmark artificial intelligence rules may only apply at the end of 2025, the European Commission said on Thursday.

Alphabet's Google, Meta Platforms, European companies such as Mistral and ASML as well as several EU governments have called for a delay in implementing the Artificial Intelligence Act, partly due to the lack of a code of practice.

Publication of the Code of Practice for large language models (GPAI), such as OpenAI's ChatGPT and similar models launched by Google and Mistral, had originally been planned for May 2.

The Commission plans to present the code in the coming days and expects companies to sign up next month and the guidance likely to kick in at the end of the year, a Commission spokesperson said.

"On the AI Act's GPAI rules, the European AI Board is discussing the timing to implement the Code of Practice, with the end of 2025 being considered," he said.

Signing up to the code is voluntary, but companies who decline to do so, as some Big Tech firms have indicated, will not benefit from the legal certainty provided to a signatory.

The Commission pushed back against calls for a delay in rolling out the AI rules.

"Our commitment to the goals of the AI Act, such as establishing harmonised risk-based rules across the EU and ensuring the safety of AI systems in the European market, remains unchanged," the spokesperson said.

Campaign group Corporate Europe Observatory decried Big Tech's role.

"Delay. Pause. Deregulate. That is Big Tech's lobby playbook to fatally weaken rules that should protect us from biased and unfair AI systems," said Bram Vranken, Corporate Europe Observatory researcher and campaigner.

The AI rules for GPAI models will become legally binding on August 2 but only enforced a year later for new models placed on the market starting from next month. Existing models will have two years to August 2, 2027 to comply with the rules.

(Reporting by Foo Yun Chee; Editing by Hugh Lawson and Marguerita Choy)