CKE Restaurants Inc. swung to a loss in its first quarter from a year-ago profit, as sales slid at the Carl’s Jr. and Hardee’s quick-service chains, operating and labor costs rose, and $20.9 million in costs surrounding its proposed acquisition were booked.

Hardee’s sales remained positive in late April and early May while those of sister brand Carl’s Jr. were still in negative territory as a result of the challenging economy in California, CKE Restaurants Inc. said Wednesday.

For the four weeks ended May 17, Carl’s Jr.’s same-store sales at company-owned units were down 5.2 percent, compared with a 6.2-percent decline for the same period a year ago. The core market for Carl’s Jr. is California, where unemployment rates remain high, the company noted.