Nigeria's national police squad is investigating Deputy Senate President Ike Ekweremadu over allegations he illegally amended the Senate rules to aide the election of certain officers. Ekweremadu's Peoples Democratic Party said the probe is an attempt by the ruling All Progressives Congress to unseat an opposition party member from a lofty position in the National Assembly, according to local media reports.

Ekweremadu and the Senate clerk, Alhaji Salisu Maikasuwa, have both been accused of forging the Senate Standing Rules days before the election of principal officers into the 8th National Assembly last month and claiming the action was approved by the previous Senate. Rumors swirled after new rules on the election of principal officers emerged at the end of the 7th National Assembly in June.

The Nigeria Police Force on Monday ordered Ekweremadu to report to police headquarters for questioning. Investigators stormed the National Assembly in Abuja to detain the Peoples Democratic Party lawmaker, but Ekweremadu was not in his office at the time. Some senators have defended him, saying the Senate rules are often changed before the new Nation Assembly is sworn in, according to Nigerian news site Vanguard.

The scandal has pitted Nigeria’s main political parties against each other. Peoples Democratic Party spokesperson Olisa Metuh expressed alarm over the police investigation and said Nigerian President Muhammadu Buhari's party was attempting to blackmail Ekweremadu so that a preferred All Progressives Congress senator could take over as deputy president.

“Our democracy is facing a serious danger. We are at the verge of a quick slide into dictatorship and the personal freedom entrenched in the polity in the last 16 years by the [Peoples Democratic Party] is about to be obliterated," Metuh said in a statement this week obtained by Nigerian newspaper THISDAY. "Since President Muhammadu Buhari’s statement that Senator Ekweremadu’s election was ‘unacceptable’ to his party, the Deputy Senate President, who can only be removed by the Senate, has come under threats and intense pressure from APC leaders to resign and allow a senator from the ruling party to take his position. However, having failed to get him to resign, the APC has now engaged in a heinous plot to force him out of office, a design, which totally negates the independence of the legislature and the spirit and letters of the Constitution of Nigeria."

The two parties struck a deal last month in which Bukola Saraki of the All Progressives Congress was elected Senate president if Ekweremadu returned as deputy Senate president. The Peoples Democratic Party's public support for Saraki, who defected from the party, could be a sign that the opposition is forming an alternative power base to crack Buhari’s administration, the Associated Press reported. Buhari allegedly called Ekweremadu's election a setback and said he was confident his All Progressives Congress would overcome it, according to Nigerian newspaper the Nation.

A number of Peoples Democratic Party members have ditched the faction for the All Progressives Congress, after Buhari defeated incumbent Goodluck Jonathan in the March 28 presidential elections. The defections have stirred fears that the opposition party will collapse and Nigeria will become essentially a one-party state, after years of lacking a viable opposition in the political landscape that was controlled by the Peoples Democratic Party. The All Progressives Congress was formed in 2013 by four opposition parties that merged to knock the Jonathan's party from its 16-year majority rule.