San Francisco officials are pressing state regulators for a public investigation of PG&E after 40 major power outages since January, according to a letter from city leaders.

Each outage affected more than 1,000 customers. More than a quarter hit the city’s west side, where a Dec. 20 blackout lasted the longest. That earlier outage cut power to a third of San Francisco.

The mayor, city attorney, Board of Supervisors president and head of the San Francisco Public Utilities Commission want the state Public Utilities Commission to examine the later outages as well as the December failure. Their letter also raises concerns about delayed infrastructure projects, two recent fires attributed to PG&E equipment and a planned sale of a SoMa substation the city has expressed interest in buying.

The state commission said its investigation of the December outage remains underway but is being conducted privately. PG&E spokesperson Tamar Sarkissian said the utility is reviewing the city’s letter and will respond as appropriate.