According to Article II, Section 3, it grants the president the authority “on extraordinary occasions, convene, both Houses, or either of them, and in case of disagreement between them, with respect to the time of adjournment, he may adjourn them to such as he shall think proper.”
Both chambers are not expected to return to the Capitol until May 4. however both the Senate and House have been conducting pro forma sessions in the meantime. Those sessions prevent Trump from making recess appointments, which he says are crucial to his administrations response to the pandemic.
In response to it never being done before he said, “Perhaps it’s never been done before, nobody’s even sure if it has," Trump said. "But we’re going to do it. We need these people here. We need people for this crisis, and we don’t want to play any more political games”