Tuesday's match-up between the New Orleans Pelicans and Dallas Mavericks and the game between the Boston Celtics and Chicago Bulls have been postponed.
The league also halted Saturday's game between the Celtics and Miami Heat.
The NBA said the postponements were made "in accordance with the league's Health and Safety Protocols" but did not elaborate, adding that it planned to meet with its players' association on later in the week to discuss modifying its health and safety protocols.
The league has said it has no plans to put its season on hold, as teams struggle to make available a league-mandated eight-man roster for games due to injuries and COVID-19 contact tracing.
After putting the season on hold in March due to the COVID-19 pandemic, the NBA organised the rest of the games in a secure "bubble" environment at Walt Disney World in Florida but started its 2020-2021 season in December with most teams playing in their home markets.