CenturyLink Inc. misled investors about its success in integrating Level 3 Communications Inc. after a 2017 merger, a March 6 suit alleged.

The telecommunications firm assured investors that the integration process was going well, according to the complaint filed in the U.S. District court for the Central District of California. But there were actually “undisclosed material weaknesses” in CenturyLink’s internal controls, delaying its 2018 financial results, the suit said.

CenturyLink initially planned to file its 2018 Form 10-K with the Securities and Exchange Commission in February, but had to push back the filing due to integration problems, the complaint said....