As I reported last month, Pierce County may ask its employees to pay for a portion of their own health insurance for the first time.

Exactly how much is subject to ongoing negotiations with unions representing county employees. But for the purposes of her proposed 2010 budget, County Executive Pat McCarthy has assumed the county’s cost of health insurance will not rise at all next year, despite an 11 percent increase in the cost of providing health insurance.

That would mean employees would have to pick up all of the increased cost, about $4 million.

But everything’s negotiable, and budget director Patrick Kenney told the County Council this morning it’s possible the result of negotiations could lead to an increase in the county’s share of health insurance costs.

“You have to do good-faith bargaining,” Kenney said at a council budget hearing.

Fair enough, council members said. But don’t’ expect the council to pay for it.

“This council won’t come up with new money to cover that contingency,” Chairman Roger Bush told Kenney, though he seemed to be speaking as much to union negotiators.

Bush spelled out his take on the likely consequences of higher county health insurance costs in stark terms. Any increase in county costs “probably would result in very rapid and large numbers of layoffs to cover the bottom line.”

Kenney suggested McCarthy thinks the same thing. He said there would be “ramifications for staffing and service levels” if employees don’t pick up all of the increased health care costs.

In an interview after the meeting, Bush made it plain he thinks the ball is in the unions’ court.