NEW YORK, June 6 (Reuters) - The Securities Industry and Financial Markets Association (SIFMA) could ask the U.S. Securities and Exchange Commission (SEC) for an extension of the current two-year implementation timeline for a rule expanding central clearing for U.S. Treasuries, said William Thum, managing director for the asset management group at SIFMA.

The SEC in December adopted new rules aimed at reducing systemic risk in the world's biggest bond market by forcing more trades through clearing houses. The rules will be implemented in phases by June 2026.

But work needed to change access models to the Fixed Income Clearing Corporation (FICC), a subsidiary of trade processor DTCC and currently the country's sole clearer for Treasuries, could require more time, Thum said. (Reporting by Davide Barbuscia Editing by Chris Reese)