KINGSTON, Jamaica (AP) — A top court ruled Wednesday that a lawmaker allied to Prime Minister Bruce Golding is ineligible to sit in parliament because she also holds U.S. citizenship.

The decision has the potential to narrow Golding's already slim majority of 31-28, depending on whether his Labor Party is ultimately able to hold onto the seat.

Under this former British colony's law, anyone with allegiance to a non-Commonwealth country is prohibited from serving in the legislature.

High Court Judge Roy Jones found Shahine Robinson cannot represent the constituency of northeast St. Ann parish even though she said she would immediately give up her U.S. citizenship.

The judge will decide by Oct. 4 whether to hold a by-election or declare the seat for the opposition People's National Party candidate defeated by Robinson in the 2007 elections.

Since the 2007 vote, there have already been three by-elections involving Labor legislators who held dual citizenship. The ruling party successfully defended each seat.

Robinson didn't acknowledge having U.S. citizenship until the opposition party challenged her status in the island's Supreme Court. Last week, she acknowledged having American citizenship since 2006.