Nurses are asking the National Labor Relations Board to schedule a vote on union membership at Memorial Medical Center.

After a contentious organizing effort, a petition for an election at the Modesto hospital was filed with NLRB on Friday. An estimated 850 registered nurses are eligible to vote on whether to join the California Nurses Association/National Nurses United.

No election date has been set but the vote could take place in about six weeks, unless the petition is challenged by the hospital’s leadership.

“We are very optimistic and hopeful we can move forward with a timely election, as the RNs deserve,” said Liz Jacobs, a union spokeswoman. “We are hopeful the hospital will do the right thing and move forward with an election date that the NLRB sets.”

In a statement Friday, Memorial said the petition seeks to make the union the exclusive bargaining representative for full-time, part-time and per diem nurses at the medical center. It has been a nonunion hospital since it was founded in 1948.

“I’m proud to work with a great group of dedicated health care professionals whose goal is to provide safe, high-quality, affordable health care,” said Chief Executive Officer Daryn Kumar. “I firmly believe we can continue to accomplish our goals without the involvement of an outside third party.”

Pro-union nurses said an effort to organize the staff began in earnest after nurses at Sutter Tracy Community Hospital voted to join the union in March 2012.

Later that year, the nurses association complained to NLRB that security guards and a house supervisor at Memorial had prevented a veteran nurse from distributing union fliers, which led to a settlement in which Memorial’s parent organization, Sutter Health of Sacramento, agreed not to impede legal organizing activity.

There were additional complaints and NLRB citations as pro-union staff asked co-workers to sign cards registering their interest in joining the union.

Some of the leading concerns at the hospital are nurse-to-patient staffing and nurses being assigned to work in clinical areas without the proper expertise, the union said.

“When we checked out the California Nurses Association, we were impressed,” said Melanie Thompson, who works in intensive care and went with a group to file the petition in Oakland. “It’s a union run by nurses.”

Thompson said that across-the-board layoffs at Memorial early last year were upsetting for employees. She said the staff was scaled down just before the busy flu season and that the hospital has since brought in large numbers of traveler nurses from other states.

The California Nurses Association/National Nurses United says it represents 185,000 members in 300 medical facilities in the United States. Its membership includes nurses at Doctors Medical Center and the Kaiser Permanente hospitals in Modesto and Manteca.

BY KEN CARLSON