TALLAHASSEE — A warning to Floridians with Citizens Property Insurance coverage: Check your mailbox.

About 300,000 customers of the state-run insurer of last resort are receiving letters in the mail this month with an offer to switch to a private insurance company.

If customers don’t respond by Oct. 5, the letters state, customers will be forced to go with the private company — at a potentially far higher cost.

A Citizens spokesperson said Tuesday that the vendor hired to print the letters has been inundated by the volume, meaning some policyholders are getting less than the customary 30 days to respond. Although the letters are typically dated Aug. 28, as many as a third of customers received them much later. A notice sent to a Miami Herald editor was postmarked Sept. 13, for example.

Some customers still haven’t been notified. Between 10,000 and 15,000 letters were sent out Tuesday, but everyone should receive the letters by Friday, Citizens spokesperson Michael Peltier said.

Because of the problem, Citizens is extending the deadline to respond to Oct. 10. Insurance agents have been alerted to the delays, he said.

“The goal is always to give policyholders at least 30 days, but vendor issues prevented that from happening,” Peltier said. “Worst case scenario is folks are going to have a couple weeks.”

If customers don’t respond in time, they could be in for an expensive surprise.

Eunic Epstein-Ortiz said she received a letter at her St. Petersburg home on Monday with an offer from Tampa-based Slide Insurance, a new startup company that has increased its footprint in Florida’s ailing property insurance market.

The offer from Slide was for a premium of $7,484 — 77% higher than the $4,227 if she stayed with Citizens, according to the notice she received.

The envelope bore no indications that an urgent deadline was inside, said Epstein-Ortiz, who ran for the state Senate last year as a Democrat representing St. Petersburg but lost.

“I am completely aware, our insurance system currently is not where it needs to be,” Epstein-Ortiz said. “But offloading 300,000 people, seemingly in the dead of night, with almost no notice, with no urgency to it, is not the way to do it.”

As insurance companies have folded or reduced their exposure in Florida in recent years, Citizens has seen its policy count grow to about 1.4 million, making it the largest insurer in the state.

To reduce Citizens’ policy count, state regulators this year have approved several companies, including Slide, to assume some of the state-run insurer’s policies. Customers don’t have to accept the private companies’ offers. But if the offer is within 20% of Citizens’ rate, customers can still decline the offer, but they can’t renew their policy with Citizens.

Policyholders who receive offers can make their choice through their agent or online at citizensfla.com/online-choice.

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Asked whether she and her wife would take up Slide’s offer, Epstein-Ortiz’s response was an immediate “no.”

“Why would we go to another insurer with worse coverage for twice the price?” she said. “It makes absolutely no sense.”