Mathematicians have issued a declaration warning of significant threats posed by artificial intelligence to the field of mathematics research, particularly concerning the integrity of proofs and the academic profession. The Leiden Declaration, developed over eight months by a working group of 16 researchers and published on June 2, 2026, with endorsement from the International Mathematical Union, highlights concerns that AI models can generate convincing yet incorrect mathematical arguments. This development risks undermining traditional standards for correctness, transparency, and verifiability of proofs, potentially cluttering academic literature with erroneous results and disproportionately impacting early-career mathematicians and students. The declaration follows OpenAI's recent announcement of an AI model disproving an 80-year-old geometry conjecture, underscoring the growing influence of tech companies in mathematical research.