INDIANAPOLIS (AP) — A new state law that went into effect on Thursday allowing employees to keep guns locked and out of sight in their vehicles while parked at work caused some confusion as the Indiana Chamber of Commerce weighed the possibility of a legal challenge.

One steel company told workers at two northwestern Indiana mills that they were not permitted to bring guns onto its property despite the new law. In a memo dated Monday, ArcelorMittal said federal law prohibits the company from having firearms at its mills at Indiana Harbor and Burns Harbor, but didn't cite the specific law.

When The Associated Press called the company to ask for more details, the company also declined to specify the law.

One provision of the state gun law says it doesn't cover situations where it conflicts with federal law. But ArcelorMittal's Lake Michigan steel mills are not mentioned, said the law's author, Rep. Robert Bischoff, D-Greendale.

"But they could be exempt under the federal exemptions," he said.

The trouble, said Indiana Chamber of Commerce president Kevin Brinegar, is that the law is inconsistent. The law includes a list of 10 exemptions, including schools, prisons, child care centers, utilities and some chemicalplants. But the list doesn't include banks, he said.

And Bill Reardon, the police chief at Indianapolis International Airport, said he believes the law allows airport employees to bring guns to work despite security concerns.

"We probably should have been included," he said. "I understand everybody's concerned over their rights, but there has to be some commonsense perspective as it relates to aviation security."

Brinegar said questions remain over whether employers can ban guns from company-owned vehicles, have workers with guns park in a separate locked lot and require employees who want to bring guns to work to prove they have a gun permit.

"It's a quagmire," said Brinegar, a former police officer who owns a handgun. "There's quite a bit of uncertainty and ambiguity with it."

He also saw a more basic issue. "What you have here with this Indiana statute is a clash of constitutional rights," pitting employers' right to control their own property against employees' gun rights, he said.

Most businesses in the Chamber see the law as infringing on their property rights, he said, and he believes legal action may be required to settle the issue. The Chamber is working with several businesses to explore the possibility of a legal challenge, Brinegar said.

National Rifle Association spokeswoman Rachel Parsons said 12 other states have similar gun laws, and federal courts have upheld such laws in Oklahoma and Florida.

She said the NRA, which lobbied for the law, was satisfied with it.

"We're happy that people can transport firearms in their cars to and from work," she said.

A lawsuit also might be the only way to determine whether ArcelorMittal is violating the new law. Bischoff said the law's enforcement is essentially up to employees who must file lawsuits if they believe their gun rights are being violated.

The Indiana General Assembly passed the bill March 4 — one day before police said a state Department of Workforce Development auditor went to his car and returned with a shotgun that he fired inside an agency office, sending other employees fleeing.