A lockout of health care workers at the Mayo Clinic hospital in Albert Lea, Minn., last Christmas in the midst of bitter contract talks may have been a violation of federal labor law, the National Labor Relations Board has ruled.

The federal agency has scheduled a July hearing for Mayo and SEIU Healthcare Minnesota, the union representing 79 hospital workers at Mayo Clinic Health System in Albert Lea.

The lockout was brought on by a one-day strike that hospital union employees, including nursing assistants, housekeepers, maintenance workers and others, held to protest stalled labor negotiations.

The Mayo Clinic said it warned union leaders that the hospital would hire replacement workers on a one-week contract if the strike was held and that striking workers would have to wait to return to their jobs.

The SEIU Healthcare Minnesota union filed an unfair labor practices complaint that alleges Mayo violated federal labor law by refusing to allow the strikers to return to work, refusing to provide information, and refusing to bargain over health and safety issues.

The NLRB’s decision Wednesday means that the complaint merits a hearing before an administrative law judge; it is not a ruling on the allegations themselves.

The two sides have a negotiating session scheduled next month.