Shares of Time Warner fell more than 2% today on concerns that US President-elect Donald Trump will make good on his vow to block a proposed $85 billion acquisition by AT&T. 

Trump has said in October that the telecommunication company's proposal to buy the owner of HBO, CNN and the Warner Bros film studio was an example of a "power structure" rigged against him and voters. 

Dealmakers said there will be an immediate slowdown in mergers and acquisitions as companies and advisers seek clues on how Trump's competition enforcement policy will take shape.

They are also anxious as to who he will choose to lead the Justice Department's antitrust division and the Federal Trade Commission. 

"I think a lot of deals will hit the pause button for a bit until we get some clarity on whether President Trump will moderate or be as disruptive as some expect," said a senior Wall Street banker. 

"It's going to be a tough environment for everything until we see how [Trump] behaves as a leader," the banker added.

The president does not directly decide if a merger is illegal under competition law and the job is done by the US Justice Department or Federal Trade Commission, which divide up the work of assessing mergers.

If one of the agencies decides to stop a deal, it must convince a judge to agree. 

AT&T's chief financial officer John Stephens said his company was looking forward to working with Trump and "optimistic" regulators would approve the deal. 

"Trump's policies had his discussions about infrastructure investment, economic development, and American innovation all fit right in with AT&T's goals," Stephens said at the Wells Fargo technology, media and telecoms conference in New York. 

AT&T offered $107.50 per share for Time Warner last month, aiming to acquire content to attract online customers. 

It has said the Department of Justice will review the deal, which likely faces intense scrutiny since lawmakers are already concerned about cable company Comcast's $30 billion acquisition of NBC Universal.