The 31-year-old right-hander, who is 0-0 with a 10.38 ERA in 13 innings for the Astros this season, rejected an assignment to Triple-A Round Rock. He will likely become a free agent and receive all of his $1.5 million salary after three days.
Backe is 31-29 with a 5.23 ERA over eight seasons with Tampa Bay and Houston, including a 9-14 mark with a 6.05 ERA for the Astros last year.
Backe was a regular member of Houston's postseason rotation in 2004 and '05, pitching well in October both years and helping the Astros reach the 2005 World Series. He tossed seven shutout innings in Game 4 of that Series against the Chicago White Sox.
The Astros also sent left-hander Tyler Lumsden outright to Triple-A Round Rock.