Caucus leaders say that the first member of the group tested positive on Friday night.
Rapid tests came back negative for everyone else, but further tests came back positive for two other members on Saturday.
More than 60 Democrats from the Texas House of Representatives left the state on private jets earlier this week to deny the GOP the quorum they need to pass bills aimed at restricting mail-in ballots and some early voting procedures.
The State House in Austin reconvened on Tuesday but the missing Democrats meant that under its rules there were not enough members present to conduct business.
Several of the Texas lawmakers posed for a picture onboard one of the planes, and critics were quick to point out that they were not wearing face masks, as is required by the federal government on commercial flights.
“The House Democratic Caucus is following all CDC guidance and protocols,” Chairman Chris Turner said in a statement.
“This is a sober reminder that Covid is still with us, and though vaccinations offer tremendous protection, we still must take necessary precautions.
“We are in touch with public health experts in Texas to provide additional guidance,” he added. “Our caucus will follow all recommendations from public health experts as we continue our work.”
During the course of the week, members of the group had meetings with Vice President Kamala Harris, Senate Majority Leader Chuck Schumer and Senator Joe Manchin. It has not been confirmed if anyone who tested positive was present.
The group’s departure from Texas came amid a wave of GOP-led efforts around the country to restrict voting in various ways. There is also a campaign from progressive Democrats to reform the US voting system at the federal level, which has stalled amid a refusal by centrist Democratic senators to change or abandon the filibuster.
If passed, the voting bills would add new restrictions on those who assist others in casting ballots, a provision criticized by disability advocates.
It would also ban “drive-thru” voting pioneered by Harris County, Texas in the November presidential election and 2020 primaries; as well as a 24-hour early voting period the county allowed at some precincts last year.
Other provisions in the bills would institute new identification requirements for mail-in voting and ban the distribution of mail-in ballot applications.
Some of the more hardline aspects of the legislation were reportedly removed in recent weeks, such as restrictions for Sunday voting hours which activists decried as a direct response to efforts by Black churches to transport voters to the polls on Sundays.