Activist investor Dan Loeb wants United Technologies to split into three companies, according to a letter from his Third Point hedge fund Friday.

"To reverse its years of underperformance and realize the full potential of its franchise assets, we believe UTC should split into three focused, standalone businesses: Otis [Elevator Company], [UTC Climate, Controls & Security], and an aerospace company ("Aerospace RemainCo") encompassing UTAS and Pratt & Whitney," the letter said.

Third Point said it took a "significant stake" in United Technologies in the fourth quarter. That position is likely about $1 billion in size, CNBC's David Faber reported.

Shares of the industrial conglomerate rose more than 1 percent in late morning trading Friday. The stock, which has a market capitalization of about $95.2 billion, is down more than 6 percent for the year so far.

"While UTC disagrees with several of the assertions contained in the Third Point letter, the company is always open to the input of shareholders," the company said in a release Friday. The Connecticut-based firm added it will complete a previously announced portfolio review this year.

United Technologies has "strong franchise assets with leading market share within each segment but the Company's shares have lagged its industrial peers (XLI Index) by approximately 45% over the last five years," Third Point said.

But the company has a "well-documented history of poor management execution — exemplified most recently by the botched ramp-up of the next-generation geared turbofan ("GTF") engine — as well as market share losses and underinvestment in key business areas," the letter said.

The hedge fund said it has initiated conversations with United Technologies' board and that CEO Greg Hayes has indicated the board is reviewing the company's portfolio.

Also in Friday's letter, Third Point disclosed its offshore fund performed slightly better than the S&P 500 in the first quarter, down 0.6 percent versus the index's 0.8 percent decline. But the Third Point Ultra fund lost 1.5 percent.

In response to increased market volatility and other shifts in the investment environment, Third Point said it has boosted short positions to about a quarter of assets under management, which stood at $17.7 billion as of March 31.