MELBOURNE, Australia — Four Australian members of Parliament resigned Wednesday after revealing they held dual citizenship, bringing the number of lawmakers forced to vacate their seats because of split national loyalties to 15 in less than a year.

The resignations came hours after the High Court ruled on Wednesday that another politician, Senator Katy Gallagher, a member of the Labor Party, was ineligible to remain in Parliament because she had not renounced her British citizenship before her election.

That decision prompted three other Labor members of Parliament — Justine Keay, Josh Wilson and Susan Lamb — and a member of the Centre Alliance, Rebekha Sharkie, to resign.

Section 44 of Australia’s Constitution bars anyone holding dual citizenship from running for office. Despite the clarity of the law, more than a dozen lawmakers, including a former deputy prime minister, have been found to hold dual citizenship in the past year, prompting their resignations.