Sole

Under Article VI, Section 17 of the 1987 Constitution, the HRET is the sole judge of all contests relating to the election, returns, and qualifications of the members of the House of Representatives.   As this Court explained in Lazatin v. House Electoral Tribunal[46]:

The use of the word “sole” emphasizes the exclusive character of the jurisdiction conferred x x x.  The exercise of the power by the Electoral Commission under the 1935 Constitution has been described as “intended to be as complete and unimpaired as if it had remained originally in the legislature” x x x. Earlier, this grant of power to the legislature was characterized by Justice Malcolm “as full, clear and complete” x x x. Under the amended 1935 Constitution, the power was unqualifiedly reposed upon the Electoral Tribunal x x x and it remained as full, clear and complete as that previously granted the legislature and the Electoral Commission x x x.  The same may be said with regard to the jurisdiction of the Electoral Tribunals under the 1987 Constitution.

http://sc.judiciary.gov.ph/jurisprudence/2011/march2011/192856.htm