A last major piece of the state of South Carolina’s anti-illegal immigration law took effect Thursday as all small businesses became subject to fines and potential shutdowns for employing illegal workers.

All businesses in the state must now check their new hires’ legal status and fire any existing workers known to be in the country illegally. The law is one of the toughest in the United States and had been applied for a year to companies with more than 100 workers.

“Every employee on the payroll, regardless of their date hired, has to be legal,” said Jim Knight, office administrator and spokesman for the Department of Labor, Licensing and Regulation. He said investigators will randomly check all companies, though auditors will focus on businesses that traditionally employ illegal workers such as landscaping and construction firms, hotels, restaurants and chicken processors.

The state Office of Immigrant Worker Compliance has more than doubled its number of investigators, to 23, as 110,000 additional businesses fall under the law.

The law takes full effect amid persisting controversy over an Arizona law that requires officers enforcing another law to question a person’s immigration status if there’s a reasonable suspicion the person is in the country illegally. South Carolina Republicans are vowing to seek a similar law next year.

The move by South Carolina lawmakers to expand the budget for the state office from $750,000 to $2 million this coming year comes even amid fiscal crisis and the layoffs of hundreds of state workers and the gutting of whole agencies. But supporters said it was crucial to crack down on illegal workers.

State Sen. Larry Martin said small business owners have long complained that they had to hire illegals to compete, or risk losing work to competitors who did so and underbid them. “No longer will they have the excuse they’ve got to do it because their competitor does it,” Martin said. Also, “there’s a degree of exploitation of illegal immigrants by unscrupulous employers. This will bring it to light.”

But employers in targeted industries say the focus on them is unfair. They’re concerned the law could drive away legal immigrants in this tourism-driven state, making it more difficult to hire people in jobs with already high turnover rates.

Legal workers could leave because they feel they’re being unjustly targeted or they fear for a family member who’s not legal, said Tom Sponseller, president of the Hospitality Association of South Carolina. “In our case, these are jobs a lot of people don’t want because it’s hot, hard work,” said Donna Shealy Foster, executive director of the South Carolina Nursery and Landscape Association.

Noting greenhouse and nursery work is South Carolina’s second-largest cash crop, she said, “When you don’t have a work force, it’s hard to put out a product.”

The law requires employers to check workers’ legality through a federal database or by hiring only workers who hold a driver’s license from South Carolina or other approved state. Otherwise they could face fines of up to $1,000 per worker, and a business repeatedly found to knowingly employ an illegal worker could be closed for months.

In the past year, 10 auditors checked 1,850 businesses and found 175 had broken the law. Most violations involved failing to verify workers within five days of hiring them. Auditors found illegal workers in 10 cases, Knight said.

The only company fined in the past year was a landscaping business with the most number of illegal workers — 11. The company paid a $11,500 fine and had to shut down for 10 days after it was cited twice, Knight said. Under the law, fines are waived for first-time violators who correct the problem within three days.