(a)
If the initiative petition is signed by voters not less in number than 10 percent of the voters in the district, where the total number of registered voters is less than 500,000, or not less in number than 5 percent of the voters in the district, where the total number of registered voters is 500,000 or more, and the petition contains a request that the ordinance be submitted immediately to a vote of the people at a special election, the district board shall do either of the following:
(1)
Adopt the ordinance, without alteration, either at the regular meeting at which the certification of the petition is presented, or within 10 days after it is presented.
(2)
Immediately order that the ordinance be submitted to the voters, without alteration, pursuant to subdivision (a) of Section 1405.
(b)
The number of registered voters referred to in subdivision (a) shall be calculated as of the time of the last report of registration by the county elections official to the Secretary of State made prior to publication or posting of the notice of intention to circulate the initiative petition.