Cynthia Coffman says Stapleton missed an April 2 party deadline to declare he would seek to qualify for the June primary at Saturday's assembly.
Claims were made that seven circulators who collected signatures for Lamborn were not Colorado residents.
The decision shakes up an already-fierce contest for the GOP nomination for governor.
Republicans said it would be a "dereliction of duty" to punt the appointment to the governor.
If safe lawmakers shoot down politically perilous bills, then vulnerable lawmakers can dodge a tough vote.
"Cities like Denver and states like California are allowing criminal aliens to run loose, to kill, murder, maim or hurt our fellow Americans, " said State Rep. Dave Williams.
Tuesday night's gatherings begin the process of deciding which candidates will represent their parties in a variety races in November.
In light of today's political climate, two prominent Coloradans have left their parties to become independent.
The $1.5 trillion package would provide steep tax cuts for businesses and the wealthy and more modest cuts for middle- and low-income families.
There are winners and losers in the GOP tax bill, including state and local governments, who have a lot at stake too.