Investors pulled more money from U.S. mutual funds last week than they have in any seven-day period in the past two and a half years.

Net redemptions reached $28.6 billion in the week ended Dec. 16, according to a statement from the Investment Company Institute, a trade group. It was the biggest weekly outflow since June 2013, ICI data show.

Some of the redemptions might reflect year-end tax-loss selling, which are sales made for tax purposes, ICI Senior Economist Shelly Antoniewicz said in the statement.

Investors withdrew $11.1 billion from stock funds, $12 billion from bond funds and $5.6 billion from funds that buy a mix of stocks and bonds. Municipal bond funds attracted $647 million, the only category that saw inflows.

Mutual funds have experienced net redemptions every month since July, according to ICI data. In each of the first six months of the year, funds gathered money.