Among Silicon Valley’s top tech employers, Facebook Inc. could be the most vulnerable to US President Donald Trump’s expected crackdown on guest-worker visas, according to a Reuters analysis of US Labor Department filings. More than 15% of Facebook’s US employees in 2016 used a temporary work visa, giving the social media leader a legal classification as an H-1B “dependent” company. That is a higher proportion than Alphabet Inc., Google, Apple Inc., Amazon.com Inc. or Microsoft Corp.