Former Uber CEO Travis Kalanick recently asked some former colleagues, including early employees still at the company, whether they would support him in a potential shareholder battle, according to one person with direct knowledge of the effort and two people briefed about it. The requests were the latest indication that Mr. Kalanick has explored how to reassert control over the company and its board after he was forced to resign six weeks ago.

Last week, Uber’s board approved rules forbidding board members from contacting Uber employees for information or assistance unless otherwise approved by the board. The decision followed a formal request in the form of a letter to the board from Uber’s management team. The management letter was triggered by Mr. Kalanick’s discussions with former colleagues that alarmed some employees, a person familiar with the matter said.