Tex. Insurance Code § 846.004

(a) For purposes of this chapter, an employee or dependent eligible for enrollment in a participating employer's health benefit plan is a late-participating employee or dependent if the individual requests enrollment after the expiration of:

(1) the initial enrollment period established under the terms of the first health benefit plan for which that employee or dependent was eligible through the participating employer; or

(2) an open enrollment period under Section 846.257.

(b) An employee or dependent is not a late-participating employee or dependent if the individual:

(1) was covered under another health benefit plan or self-funded employer health benefit plan at the time the individual was eligible to enroll;

(2) declined enrollment in writing, at the time of the initial eligibility for enrollment, stating that coverage under another health benefit plan or self-funded employer health benefit plan was the reason for declining enrollment;

(3) has lost coverage under the other health benefit plan or self-funded employer health benefit plan as a result of:

(A) the termination of employment;

(B) a reduction in the number of hours of employment;

(C) the termination of the other plan's coverage;

(D) the termination of contributions toward the premium made by the employer; or

(E) the death of a spouse or divorce; and

(4) requests enrollment not later than the 31st day after the date coverage under the other health benefit plan or self-funded employer health benefit plan terminates.

(c) An employee or dependent is also not a late-participating employee or dependent if the individual is:

(1) employed by an employer that offers multiple health benefit plans and the individual elects a different health benefit plan during an open enrollment period under Section 846.257;

(2) a spouse for whom a court has ordered coverage under a covered employee's plan and the request for enrollment of the spouse is made not later than the 31st day after the date the court order is issued; or

(3) a child for whom a court has ordered coverage under a covered employee's plan and the request for enrollment is made not later than the 31st day after the date the employer receives the court order.