President Donald Trump has fired one of two Democratic members of the U.S. Surface Transportation Board to break a 2-2 tie before the body considers the largest railroad merger ever proposed.

Board member Robert Primus said on LinkedIn that he received an email from the White House Wednesday night terminating the position he has held since he was appointed by Trump in his first term. The vacancy would allow Trump to appoint two additional Republicans to the board before its decision on the Union Pacific-Norfolk Southern merger though the Senate would have to confirm them.

Primus was named Board Chairman last year by former President Joe Biden and he was the only board member to oppose Canadian Pacific's acquisition of Kansas City Southern railroad two years ago when it was approved. Trump elevated Board member Patrick Fuchs to Chairman after he was elected.

This follows Trump's previous firings of board members at the National Transportation Safety Board, Federal Reserve, Equal Employment Opportunity Commission and Nuclear Regulatory Commission, which are all supposed to be independent agencies.

"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."

Primus said the firing is "deeply troubling and legally invalid" so he plans to continue serving until he is blocked and then he will consider legal actions to fight it. Primus has already been removed from the STB website.

"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. "My record during my four and a half years at the board reflects this and I strongly believe the actions of the White House would weaken the board and adversely affect the freight rail network in a way that may ultimately hurt consumers and the economy."

The nation's largest railroad union that represents conductors, SMART-TD, quickly condemned the firing.

"The explanation provided for this decision -- that his position has been "eliminated" -- is nothing short of outrageous. Appointed bodies established through federal code are not designed to be erased at the whim of powerful corporate interests," the union said. "This action is unprecedented, unlawful in spirit, and reeks of direct interference from hedge funds and the nation's largest rail carriers."

The board is set to consider Union Pacific's $85 billion acquisition of Norfolk Southern in the next two years before deciding whether to approve the nation's first transcontinental railroad and reduce the number of major freight railroads in the U.S. to five.