Beginning Sept. 14, businesses that continue to employ workers whose Social Security numbers don't match government records can expect to receive letters from the U.S. Department of Homeland Security.

If the discrepancies aren't cleared up within 90 days, employers must fire the workers or face fines of up to $10,000 per offense, according to a rule the Bush administration announced Aug. 11. The rule is aimed at exposing illegal immigrants who are using fraudulent documents.

For Florida agriculture, the timing couldn't be much worse.

The vegetable planting season and the citrus harvest season begin in September. Labor shortages are a possibility, some say, and not just for growers.

"This really exacerbates an already serious situation. This past season was not as bad as it could have been because the construction industry slowed down," said Lisa Lochridge, a spokeswoman for the Florida Fruit and Vegetable Association, based in Maitland.

"The consequences are going to be felt pretty seriously," she said Friday. "Construction, hospitality and agriculture -- that is the three-legged stool of our state economy, and all three depend on this workforce. It is going to be very tough."

J. Luis Rodriguez, trade adviser for Florida Farmers Inc. in Lake Worth, agreed.

"We are in a hell of a bind with this workforce," Rodriguez said. "Unless they have some foolproof ID, all we can do is look at the Social Security number."

With uncertainty about this season's labor supply, more growers are turning to the federal H-2A visa program, which allows companies to bring in foreign laborers as guest workers. Growers must provide furnished housing, meals or a place to cook them and, in Florida, pay workers $8.56 an hour, said Roy Hefty, operations manager at Memphis-based H2A USA, which has an office in Lakeland.

The company has handled guest workers for the construction industry for 20 years.

"Housing is the biggest issue we have," Hefty said. "If the crackdown occurs, it is going to have huge repercussions for everybody, not just farmers."

Last year, H2A USA brought in nearly 300 H-2A workers for Florida's citrus industry. This year, the company expects to bring in 600 to 1,000 workers from Mexico to pick the state's citrus.

"I have had calls from 20 states," Hefty said. "People want something next week. We tell them this is a four- to six-month project. You start six months before you need workers."

Charles Lucas, president of Fort Myers-based Consolidated Citrus LP, the nation's largest citrus grower, said the company relies on independent labor contractors and selects those who are using the H-2A
program.

This year, to better understand H-2A, the company plans to obtain a couple of H-2A crews on its own.

"Labor is becoming a big concern. There's no question that there's a lot of uncertainty," Lucas said. "As an industry, we don't know how many workers are still available. It's not just Florida, it's the entire U.S."

The fruit and vegetable association supplied more than 3,000 H-2A workers for Florida's fields during the 2006-07 season, said Walter Kates, the group's labor division director.

He said H-2A "is not an easy program."

"My guess is there will probably be more H-2A workers this year," Kates said. "It's too early to tell."

Greg Schell, attorney with the Migrant Farmworker Justice Project in Lake Worth, said many of the state's largest growers have indicated to him they plan to use more H-2A workers this season.

With the availability of workers uncertain, companies such as Southern Gardens Citrus outside Clewiston are evaluating their options and plan to harvest as much fruit as possible with mechanical harvesters, spokeswoman Judy Sanchez said.

"The only certainty you have is that you are going to have a citrus crop and you have a finite amount of time to harvest that crop," Sanchez said. "You have to have labor."

Lochridge said the tighter rules on Social Security numbers won't solve the illegal immigration problem and will lead to "chaos and hardship."

"Good employers will be stuck between a rock and a hard place," she said. "If they comply, they stand to lose a big chunk of their workforce. If they don't, they face stiff fines."