By Jeffrey Dastin and Uday Sampath Kumar (Reuters) -Amazon.com Inc’s layoffs will now include more than 18,000 roles as part of a workforce reduction it previously disclosed, Chief Executive Andy Jassy said in a public staff note on Wednesday. The layoff decisions, which Amazon will communicate starting Jan. 18, will largely impact the company’s e-commerce and human resources organizations, he said. The cuts amount to 6% of Amazon’s roughly 300,000-person corporate workforce and represent a swift turn for a retailer that recently doubled its base pay ceiling to compete more aggressively for ta…