Carl Icahn, billionaire activist investor and former advisor to President Donald Trump, made headlines in recent days for having sold off shares of Manitowoc Company (MTW) ahead of an announcement by the Trump administration that new tariffs would take effect.

Shares of the crane manufacturing company dropped 4.8% on February 16, shortly after Commerce Secretary Wilbur Ross released the "Steel and Aluminum 232" reports on the same day, according to CNBC. These reports suggested a global tariff of 24% or more on all steel imports. (See also: Which Stocks Will Win or Lose From Steel, Aluminum Tariffs?)

Icahn's move has been questioned by some analysts, who claim the billionaire mogul may have acted on insider information. Icahn has responded to the allegations by saying they're "categorically untrue."

'Legitimate Investment Reasons'

A statement from representatives for Icahn said "the recent media speculation regarding our sale of Manitowoc stock calls for a response. We state for the record:

"Any suggestion that we had prior knowledge of the Trump administration's announcement of new tariffs on steel imports is categorically untrue. We reduced our position in Manitowoc for legitimate investment reasons having nothing to do with that announcement."

Manitowoc and other construction equipment manufacturers rely heavily on steel in their manufacturing work. The fact that Icahn sold off shares just before the announcement and the drop in the company's stock price looked suspicious to some critics, who assumed that he must have known the tariff announcement was coming. No one has come forward with any evidence of these claims.

Icahn Sold One-Third of Stake

According to a filing with the SEC, investment entities which Icahn controls sold off one-third of all their stock in Manitowoc between February 12th and February 22 of this year. This decrease in position amounted to roughly 940,000 shares, sold at $32 to $34 per share, for a total of roughly $31 million.

Despite the massive sell-off, even after shedding almost a million shares, Icahn still owns 4.85% of MTW, which is down from his previous stake of 7.5%. Icahn was special advisor on regulation to the Trump administration, although he resigned from the position in August 2017.

MTW stock suffered an immediate 4.8% drop after Secretary Ross' announcement. It then fell another 6% last week after President Trump announced plans to impose a 25% tariff on steel and 10% on aluminum.

Allegations of insider trading are not taken lightly by regulators. Billionaire Steven A. Cohen was implicated in insider trading activities associated with a hedge fund he controlled and was subsequently banned from trading outside investor money for several years. There has been no further information about an ongoing investigation in Icahn's case, however.