Yes, IELTS scores are required to apply for a UK work permit. They demonstrate your proficiency in the English language needed to live and work in the UK. If you are applying for a UK Skilled Worker visa, you must obtain a minimum CEFR level B1 or an equivalent IELTS score of 4.0, with a minimum of 4.0 bands in each skill.
You can also demonstrate your proficiency in the English language through other standardized English language tests.