The world’s largest money manager, BlackRock, has jumped into the fee war alongside giants such as Fidelity and Vanguard, and investors may be the winners.

BlackRock blk , with $4.9 trillion in assets under management, lowered the prices for 15 of the firm’s most popular U.S. exchange traded funds (ETFs). The reason was most likely new federal rules on retirement savings that requires advisors put the interests of their clients first. BlackRock appears to be betting that the rule will make ETFs an even more popular option in retirement accounts, and therefore an even more competitive segment in the money management industry.

ETFs, which trade stocks but mimic the returns of the shares in a particular industry, geography or market in general, have gained steam over the past decade since the investment vehicles are generally cheaper than mutual funds. ETFs, since they generally follow passive indexes, also tend to outperforms most actively managed funds.

“This is another critical milestone to help advisors as they prepare for the major shift the Department of Labor fiduciary rule requires—providing investors with quality index exposures at great value in the center of their portfolios,” said Salim Ramji, head of BlackRock’s U.S. wealth advisory business, in a statement Wednesday.

(Related: How the Family that Runs Fidelity Uses A Private VC Fund to Pocket Millions off of Americans’ 401(k)s)

The fee decrease affects $216 billion in assets, about 17% of $1.3 trillion BlackRock manages in its iShares ETF line. BlackRock slashed the fees on one of its most widely used ETFs, stock market index tracker iShares Core S&P 500 ETF, to 0.04% from 0.07%.


The cost of the most expensive BlackRock ETF to see its fees cut, the MSCI Emerging Markets ETF, fell from 0.16% to 0.14%.

That’s good news for investors as money managers play a game of limbo with their fees. Other money managers such as State Street Global Advisors and Vanguard have revealed lower fees. In June, Fidelity lowered expenses on 27 of its index mutual funds and ETFs to an average of 0.102% from 0.116%.

“We are taking already one of the lowest cost index fund offerings in the industry and making it even more compelling,” said Colby Penzone, senior vice president for Fidelity’s Investment Product Group in a statement at the time.

In comparison, State Street’s SPDR S&P 500 ETF carries a fee of 0.09% versus BlackRock’s 0.04% for a similar fund, while other ETFs also tracking the S&P 500 charge 0.36% of assets annually on average, according to Morningstar.

BlackRock, for its part, also seems to have ambitions to dominate the fast-growing ETF market. Mark Weidman, the global head of iShares, told the Wall Street Journal that it hopes to make its S&P 500 ETF “the biggest in the world.”

That title currently belongs to State Street’s SPDR S&P 500 ETF with about $197 billion under management.

In 2015, BlackRock managed 39% of all ETF assets, followed by Vanguard, which managed 23%.