Whitburn and Blackburn residents’ area facing a second by-election in a year after it was confirmed local Labour councillor David Russell had resigned.
Councillor Russell handed his resignation to Graham Hope, the council’s Chief Executive on Monday morning.
It is understood he has also quit the Labour party.
No reason has been given for his decision and Mr Russell has not responded to requests from the Local Democracy Reporting Service (LDRS) for a statement.
It is a blow for the minority Labour-led administration however, which will see its headcount reduced to just 11 councillors, including fellow Whitburn councillor George Paul.
Labour runs the West Lothian administration in a loose “confidence and supply” agreement, backed by four Conservatives, one Lib Dem and one Independent