Caterpilar's statement indicates that their policy on ensuring the correct procedures are upheld within their supply chain is that of a self-assessment which the suppliers must adhere to and carry out themselves, (stated in the passage headed 'Verification').
"Caterpillar Inc., including its majority owned subsidiaries, of which Progress Rail Services UK Limited is one, and joint ventures and following a transition period, newly acquired companies ("Caterpillar"), is committed to respecting internationally recognized human rights throughout its global operations, as noted in our Human Rights Policy and our Supplier Code of Conduct, both of which are publicly available. Caterpillar’s Human Rights Policy, which was developed taking into consideration principles in the United Nations Declaration of Human Rights and the International Labor Organization's Declaration on Fundamental Principles and Rights at Work, applies tothe entire Caterpillar enterprise.Suppliers are an essential part of Caterpillar's extended value chain and Caterpillar is committed to working with them to uphold the principles in our Values in Action, Supplier Code of Conduct and Human Rights Policy."
"We require a selection of our suppliers to complete a self-assessment, requesting information on a number of issues set out in our Supplier Code of Conduct, including human rights, .such as policies and procedures they have in place to tackle slavery and human trafficking in their own supply chain"
"Our standard purchase order terms and conditions require that suppliers comply with our Supplier Code of Conduct, including an expectation that our suppliers conduct all business in a manner that respects human rights. "