Islamabad, Pakistan - Pakistan is boycotting a United Nations-sponsored inter-parliamentary event in the United States, in protest against an "undue delay" in a visa issuance by the US to its senate deputy chairman, a statement said.

Pakistani Senate Chairman Raza Rabbani took "serious notice of undue delay in the issuance of visa to deputy chairman of Senate Molana Abdul Ghafoor Haideri by the US Embassy in Islamabad", said the statement released on Saturday evening.

Haideri was one of two Pakistani senators scheduled to travel to the US to attend the Inter-Parliamentary Union's (IPU) hearings on environmental issues at the UN headquarters in New York City, scheduled to be held on February 13 and 14.

Haideri and fellow Senator Salahuddin Tirmizi were due to fly out of the Pakistani capital, Islamabad, on Sunday, according to the Pakistani Dawn newspaper.

Tirmizi's visa was granted, Dawn reported, but Senate Chairman Rabbani cancelled the trip due to the non-issuance of Haideri's visa in time. Rabbani went further still, barring senators from visiting the US or meeting any US officials until the issue is resolved.

"The Chairman Senate has further directed that no Senate delegation will visit USA unless an explanation to the delay in issuance of Visa to the Deputy Chairman Senate is given by the US Government/Embassy of USA in Pakistan," said the statement.

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Haideri belongs to the right-wing religious Jamaat Ulema Islam party's Fazl faction (JUI-F), and has been a senator since 2008, representing the Balochistan district of Kalat in the lower house of parliamentary previously.

The JUI-F and its leader, Fazl-ur-Rehman, are known for being religiously conservative, following a strict literalist interpretation of Islam known as the Deobandi school. Rehman has several times criticised the US in public and in parliament for its policies in the region.

Haideri himself was jailed in 2001 for five months for leading a protest movement against Pakistan aiding the US-led war in neighbouring Afghanistan.

Pakistan is not among the seven Muslim-majority countries from which US President Donald Trump has attempted to block immigration. Trump has, however, promised that visa applicants from Pakistan and Afghanistan would face "extreme vetting", although it remains unclear what this entails.

Haideri did not apply for the visa personally, rather his application was submitted by Pakistan's senate secretariat, said Noor Ahmed Kakar, a spokesman for Haideri.

Kakar offered no comment to Al Jazeera on the delay in issuing the visa.

Fleur Cowan, the spokesperson for the US embassy in Islamabad, told Al Jazeera that the embassy was not in a position to offer comment on individual visa applications due to privacy laws.

Asad Hashim is Al Jazeera English's Web Correspondent in Islamabad. He tweets @AsadHashim.