A federal judge in Chicago has issued a temporary restraining order forbidding Alliant Insurance Services Inc. from soliciting Aon construction services group employees and clients.

The ruling is the latest in disputes between Aon and Alliant about alleged poaching.

In a lawsuit filed earlier this month, Aon alleged that former executive Michael Heffernan resigned abruptly from Aon; immediately joined Newport Beach, California-based Alliant; and that he helped hire away 26 of the 31 employees at Aon's San Jose, California, office.

Alliant announced earlier this month that Mr. Heffernan had joined it as vice president of its construction services group in San Jose.

In her Feb. 10 ruling in Aon P.L.C. v. Michael Heffernan et al., U.S. District Court Judge Andrea R. Wood approved the temporary restraining order, saying Aon had “demonstrated a reasonable likelihood of success on the merits of their claims, starting with the choice of which state's law should apply.”

Although Alliant argued the case should be heard in California, “plaintiffs have presented a sufficient legal and factual argument in favor of Illinois law to support the likelihood of success on the merits of their claims,” Judge Wood ruled.

The order states also that Aon has presented evidence that it maintains a proprietary database of customer information,and that while Mr. Heffernan did not typically use it, “he accessed it for an extended period” when he began to discuss future employment with Alliant.

Aon's suit accuses Mr. Heffernan of breach of noncompete agreements and breach of his fiduciary duties. Aside from barring Alliant from soliciting any employee or client of Aon's, the judge also ordered Mr. Heffernan and others not to disclose any of Aon's information and return information from its proprietary database to Aon.

An Alliant spokesman could not be reached for comment.

A status hearing has been set for Feb. 22 in the case.

In another poaching dispute between Aon and Alliant, a New York appellate court in 2013 forbade Alliant Senior Managing Director Peter Arkley, formerly CEO of Aon's construction operations, from soliciting business from any former Aon client for the two years prior to June 13, 2011.