President Donald Trump's plans to require all U.S. pipelines to be made from U.S. steel have dropped out of the public discourse for months, leaving pipeline operators in the dark about the proposal's future.

The proposed policy has been a source of concern for the pipeline industry, but with the absence of information, it is unclear when or if it will go into effect. A January 2017 executive order directed the U.S. Department of Commerce to devise a policy requiring projects that build, expand, retrofit and repair pipelines to use material and equipment produced in the U.S. to the "maximum extent possible." Little has been heard from the White House since.

The order called for the Commerce Department to submit its policy plan within six months. As required, the department submitted its report to the White House in 2017, the agency said in a recent email. The agency declined to comment on whether the department had received any word on the next steps.

The White House did not respond to a request for comment.

Pipeline and steel industry associations contacted for this article said they were not aware of any movement on the policy.

Before the Department of Commerce filed the report with the White House, it took input from interested groups. The oil and gas industry and the pipeline sector expressed concerns about the proposed mandate. The Interstate Natural Gas Association of America, the American Petroleum Institute, the Association of Oil Pipelines and other groups said there are constraints in the U.S. that limit pipeline companies' ability to get the materials they need from domestic sources alone.

An ICF International study, commissioned by pipeline trade groups, found that about 77% of the steel used in line pipe was imported in one form or another. Detailed material specifications exist for pipe building, which means that pipeline operators and developers cannot simply substitute materials when they build and repair, ICF said. The study said breaking the international supply chain would have a disruptive effect on the pipelines sector.