The Trump administration moved on Monday night to block investments in Chinese stocks by a government retirement savings fund.

National Economic Council Director Larry Kudlow and National Security Adviser Robert O’Brien made the administration’s wishes known in a letter to Labor Secretary Eugene Scalia, according to a person familiar with the matter.

Scalia sent a letter to Michael Kennedy, the chairman of the Federal Retirement Thrift Investment Board, telling him to “halt all steps” associated with putting government employees’ money in a fund that includes stakes in Chinese companies, according to a copy of the letter obtained by Bloomberg News.

President Donald Trump has faulted China over the spread of the coronavirus, and questions have arisen over how faithfully the Beijing government will adhere to a recent trade agreement between the two countries. Trump has mused about punishing China for the outbreak, and the move to curtail retirement investments appears to be the first tangible step.

The Thrift Savings Plan -- the federal government’s retirement savings fund -- was scheduled to transfer roughly $50 billion of its international fund to mirror an MSCI All Country World Index, which captures emerging markets including China.

“There’s a security angle here,” O’Brien said Tuesday in an interview on Fox Business Network. He said about $5 billion of the fund would have been invested in Chinese firms. “A number of the companies they were going to be invested in were Chinese military companies or surveillance state companies. We thought that was risky for U.S. national security, but we also thought it was risky for the investors.”

O’Brien said the administration did not want to potentially fund aircraft manufacturers who do work for the Chinese military or surveillance firms that support what he called “concentration camps” for Uighur Muslims, an oppressed group in China. He also cited telecommunications firm ZTE Corp. as a company the U.S. does not want to support. “So it just wasn’t a good situation for us,” he said.

He downplayed the risk of Chinese retaliation when asked whether the measure may dampen Chinese demand for U.S. debt. “This is the safest place for anyone to put their money including the Chinese, so I’m not too concerned about that issue,” O’Brien said.

The Federal Retirement Thrift Investment Board oversees the fund and made a decision in 2017 that the money should be moved by mid-2020. Opponents of the transfer in recent weeks have engaged in a last-minute effort to stop it.

In the letter, Scalia said that O’Brien and Kudlow had “expressed grave concerns with the planned investment on grounds of both investment risk and national security.”

“As you know, the concerns expressed in this letter have been voiced by both Republican and Democratic members of Congress,” Scalia wrote in his letter to Kennedy.

The letter to Scalia was reported earlier by Fox Business Network.

--With assistance from Josh Wingrove.

This article was provided by Bloomberg News.