black mastic on plywood subfloor

1960's bathroom gutting floor, multiple layers subfloor. Ran into thin plywood layer that appears to have black mastic (no tiles, they were already removed by someone in the past). Presuming mastic may contain asbestos so holding off. Not looking to scrape it, just remove the entire plywood, but the mastic is dry and old and cracking in some areas. May need to make a cut or two, but otherwise just prying up nails. Any advice on how to proceed? Small area, less than 35 Sq Ft..