Charles Schwab is restricting access to a popular tax-sensitive investing strategy deployed by registered investment advisors that use Schwab's trading platform and other services.

The company told RIAs this week that clients will now have to have a minimum of $10 million of assets to fund long/short separately managed accounts. That is up from $1 million. In addition, portfolio margin accounts will no longer be eligible for new client enrollments or transfers of assets into long/short strategies, the company told advisors. Investors who use margin are borrowing money from their brokerage firm.

A Schwab representative said in a statement: "We regularly review our platform requirements to ensure we can effectively serve advisors and their clients across the full range of capabilities they rely on." The company says the changes apply only to new accounts. "Current clients will continue with no impact to existing terms," according to Schwab. "We remain committed to helping advisors meet client needs through a broad range of tax-aware investment solutions."

The policy change, effective Sept. 16, was previously reported by Bloomberg News.

Schwab is the nation's largest custodian for RIAs, safeguarding client assets on their behalf and providing advisors with other services such as lending. Of the company's approximately $13.1 trillion in client assets as of June 30, $5.7 trillion was in its Advisor Services unit.

Advisor demand for long/short strategies has been rising as they increasingly seek to help wealthy clients who have large concentrated positions manage their tax exposure.

Schwab has said that it was winning more business with RIAs by providing this offering.

On the company's quarterly earnings call on July 21, Chief Financial Officer Michael Verdeschi said Schwab could meet the rising demand, but cautioned that it remained a small sliver of Schwab's overall business. "While it's grown very quickly, it's still a relatively small percentage-a very small percentage of our economics," he told analysts. "It's roughly 1% of our revenue. But we stand ready to support it."