The administration of President Donald Trump dismissed a Democratic member of the Surface Transportation Board (STB), the US rail regulator charged with weighing a mega-merger between Class I carriers Union Pacific (UP) and Norfolk Southern to create the first US transcontinental railroad.

Robert Primus, one of two Democratic members of the STB, said he received an email from the White House late on 27 August "purporting to terminate my position at the Surface Transportation Board."

The move is "deeply troubling and legally invalid," Primus said in a posting on LinkedIn, and "comes at a time when the Board is considering significant pressing matters of critical importance to both our national freight rail network and supply chain."

"Robert Primus did not align with the President's America First agenda, and was terminated from his position by the White House," White House spokesman Kush Desai said. "The Administration intends to nominate new, more qualified members to the Surface Transportation Board in short order."

The action leaves the STB with three members, two Republicans and one Democrat, and two short of its five-member capacity.

Primus did not refer specifically to UP's $85bn bid to purchase Norfolk Southern. If approved by the STB, that deal would create the first transcontinental US carrier, with a new $250bn entity connecting 50,000 miles of track across 43 states.

Primus was the sole dissenter when the STB in March 2023 voted 4-1 to approve Canadian Pacific's $31bn merger with Kansas City Southern, creating the largest single US rail operator and the only railroad that links the US, Canada and Mexico. Primus cited concerns about industry consolidation and the impact on rail service. No STB board members have weighed in publicly about the prospects for the UP-Norfolk Southern merger.

SMART-TD, a railroad union that represents conductors, condemned Primus's dismissal as unjustified, and said it was likely motivated by White House concerns that Primus would oppose the UP-Norfolk Southern deal.

"This action is unprecedented, unlawful in spirit, and reeks of direct interference from hedge funds and the nation's largest rail carriers," the union said.

Primus was nominated during Trump's first term to serve on the STB and was renominated by former president Joe Biden. Primus said he would explore his legal options if he was not permitted to continue serving on the STB.

"I have worked tirelessly to build bipartisan trust and have demonstrated myself to be truly an independent Board member that has consistently rendered fair and impartial decisions," Primus said.

By Chris Baltimore