The truth is that Biden explicitly supported sick leave for the workers. Your claim that his motive was to deny them sick leave is false.
"As a proud pro-labor President, I am reluctant to override the ratification procedures and the views of those who voted against the agreement," he said in a statement. "But in this case – where the economic impact of a shutdown would hurt millions of other working people and families – I believe Congress must use its powers to adopt this deal."
"I've supported paid sick leave for a long time. I'm going to continue that fight 'til we succeed."
https://www.npr.org/2022/12/02/1140265413/rail-workers-biden-unions-freight-railroads-averted-strike