Four Democrats and one Republican are running in a Feb. 12 special election to replace Justin Rodriguez as Texas House representative for District 125.
Thirteen groups issues the warning, and some are considering suing the State.
On Saturday morning, Mayor Ron Nirenberg urged supporters to help get out the vote.
The Trump administration no longer supports requiring Texas to obtain federal approval of changes to its legislative and congressional maps.
The filing period opens Wednesday and runs through Friday, Feb. 15, at 5 p.m.
The seat in HD 125 became vacant when Justin Rodriguez was sworn in as Bexar County Commissioner, triggering a special election for his former office in the Texas Legislature.
Bexar County Elections Department has been using voting machines that are well past the typical 10-year life span.
The appointee, to be selected Thursday by City Council, will serve until a new council member is installed following the May 4 municipal elections.
Candidate filing closes on Jan. 14, and early voting begins Jan. 28.
City Council will review the applications and appoint an interim council member for District 2 to fill the remainder of William “Cruz” Shaw’s term.