The National Railway Labor Conference and The Brotherhood of Maintenance of Way Employees Division of the International Brotherhood of Teamsters (BMWED) are drawing their lines in the sand after President Joe Biden called on Congress to pass legislation that would enforce the tentative rail labor agreement.

"Additionally, passing legislation to adopt tentative agreements that exclude paid sick leave for railroad workers will not address rail service issues.

The posturing from the NRLC and the unions came after President Biden called on Congress to pass the tentative agreement on Monday night.

In a press conference on rail preparations, Association of American Railroads (AAR) President and CEO Ian Jefferies told reporters that, "If the unions are interested in a holistic discussion for structural changes as it relates to their sick time, I think absolutely the railroad carriers would be up for a holistic discussion but [they] have not done it in the zero hour.".

This would bring a total of three personal days for railroad workers.

Brendan Branon, National Railway Labor Conference chairman, told CNBC the future of collective bargaining is in the hands of Congress and urged that the legislation they pass follow the recommendations of the PEB, a board created by Biden in July to resolve the ongoing dispute between major freight rail carriers and their unions.

"There's any number of arbitrators and PEBs who have recognized that this is not only acceptable, this is the most appropriate form to settle complex negotiations, especially multi-employer, multi-craft agreements." Branon said a number of industries including the railroads have developed a set of clear practices in bargaining and the additional negotiating by the unions after the tentative agreement departs from the framework recommended by the PEB.

"Departing from a pattern would establish a precedent that there's still a better outcome achievable and I think it would pose significant stress and risk for collective bargaining in the future for the railroad industry," Branon said.

Railroad unions that voted for ratification have said they will not cross the picket lines and will support their fellow union workers, posing the risk of a nationwide freight rail shutdown.

According to federal safety measures, railroad carriers begin prepping for a strike seven days before the strike date.