MONTPELIER — The merger of Vermont’s two largest utilities may cause rates to rise slightly for another one.

Central Vermont Public Service Corp. and Green Mountain Power want to impose a new, single transmission rate for the electricity it carries on its lines for other companies.

Vermont Public Radio reported that could mean a 1.25 percent increase in rates for Washington Electric Co-op. Manager Avram Patt says Washington doesn’t believe it should be paying for increases caused simply by the merger itself.

Green Mountain Power said it would cut rates for its own customers by 0.4 percent. Patt says the merger will have the opposite effect on the 10,500 member co-op.

A GMP spokeswoman says the company hasn’t filed for new transmission rates since 1996.