PORTLAND – A group of shareholders opposed to the proposed sale of Ocean National Bank has filed a federal lawsuit to delay a vote on the sale.

The lawsuit in U.S. District Court in Portland was filed by three stockholders from New Hampshire and New York. They claim the bank has been hindering their attempts to communicate with other shareholders who might be opposed to the sale.

Chittenden Corp. of Burlington, Vt., has proposed buying Ocean National for $53.25 million. The merger is slated for a shareholder vote on Dec. 12, but the suit seeks to delay that vote by at least a week.

Ocean National is headquartered in Kennebunk with 11 branches in York County and coastal New Hampshire. It was founded in 1854 and bills itself as Maine’s oldest commercial bank.

Chittenden last January bought Maine Bank and Trust, the community bank launched in 1991 by millionaire Elizabeth Noyce of Bremen.