A trio of senators on Monday demanded a Government Accountability Office investigation into the Trump administration's system for awarding exemptions to President Trump's steel and aluminum tariffs, citing fears about the fairness of the process.

"[T]he Senate Finance Committee and industry groups have called on Commerce to clarify the criteria it uses to determine whether to grant an exclusion from the tariffs," wrote Sens. Pat Toomey, R-Pa., Tom Carper, D-Del., and Doug Jones, D-Ala., in a letter to Comptroller General Gene Dodaro.

The senators argued that the process for granting tariffs exemptions is unfair to the business community, saying that some businesses are worried about the backlog of requests for breaks and that some small businesses are struggling with red tape.

The senators called on the GAO to look into the specifics of the process, such as what feedback stakeholders can give to the federal government, the criteria used to approve or deny a request, and the average time involved resolving a request, among other details.

The administration officially instituted tariffs of 25 percent on steel and 10 percent on aluminum in March, arguing they were needed to protect domestic industries which contribute to national defense. The tariffs cover all imports, but the administration grants exclusions on a case-by-case basis if it decides that doing so wouldn’t harm “national security” — that is, because the product isn’t available domestically otherwise.

As of Nov. 12, 48,602 steel and 6,504 aluminum exclusion requests have been filed, according to the department. Of those, it has approved 12,356 requests regarding steel, or about one-in-four. It has approved about 830 ones for aluminum, or about one-in-eight. The Commerce Department currently has an estimated 100 staffers and contractors working on processing exclusion requests, according to information provided to the Washington Examiner by the administration. The process has been slow due to the fact that the tariffs are new and the department previously never had to deal with such requests.

Other lawmakers have raised questions about the transparency and fairness of the process. In late October, Commerce Department's Office of the Inspector General launched a probe into how the decisions were being made following complaints by lawmakers such as Sen. Elizabeth Warren, D-Mass.