The union representing 660 nurses at Santa Rosa Memorial Hospital has warned administrators that nurses may go on strike Oct. 2, two days after their labor contract expires.

The Santa Rosa-based Staff Nurses Association said Friday that its nurses will now vote on whether to stage a three-day walkout. If approved, the strike will begin at 5 a.m. on Oct. 2 and conclude at 5 a.m. on Oct. 5.

Both hospital administrators and the nurses union said they have disagreements over a number of labor issues, including pension benefits and on-call and night shift pay.

In a statement released Friday afternoon, the nurses union said hospital administrators are proposing, among other things, a cut in night shift pay and decrease in on-call pay. The union said the hospital is also trying to take away the union's right to negotiate benefits.

Debra Miller, vice president of human resources for St. Joseph Health Sonoma County, which runs Memorial Hospital, said the proposed changes to nurses' benefits are "not out of the realm of what other employers are doing," including local governments.

In these tough economic times, she said, the hospital must take steps to bring its costs in line with its targets to ensure its financial stability.

Miller said the hospital has proposed reducing the night differential, the extra amount paid for working the night shift, from 25 to 15 percent of regular pay. Also, the hospital proposes reducing on-call pay from 50 to 30 percent of regular pay.

The union said the proposed cuts come at a time when the hospital is reporting a $38 million operating margin for the fiscal year ended June 30.

But Miller said that its current operating margin is about 6 percent, which is about what the hospital needs to invest in new technology and remain competitive.

"A new MRI machine can cost anywhere from $2 to $3 million," she said.

The nurses union has proposed improvements to extended sick leave, retiree medical benefits (which it says are currently sub-market) and paid time-off. The changes would bring nurses' benefits in line with other hospitals.

In its statement released Friday, the union said it has proposed a 5 percent wage increase beginning Oct. 1 and 7 percent a year later. The increases would barely keep nurses' wages competitive with the lower tier of wages in the Bay Area, it said.

Miller said hospital administrators will continue to negotiate with the nurses union through next week and next weekend. The contract expires at midnight Sept. 30.

The nurses union has filed notices of intent to strike several times just before its contract was set to expire, Miller said.

"In 2010, we received the same notice on Sept. 23," she said. "We bargained until Sept. 30, came to an agreement and the union rescinded the strike."

Miller said that during the last six rounds of contract negotiations, the nurses union has filed five strike notices without striking once.