The decision to leave the task force was taken after the US-led operation refused to pay for fuel for the patrolling warships as part of a previous agreement, two highly-placed military officials told Al Jazeera on the condition of anonymity.
Military officials believe that CTF nations will feel Pakistan's absence because of its counter-piracy expertise and the Pakistani vessels' access to waters that are not friendly to Western flag-bearing ships.
Pakistan has taken command of the task force several times since 2013 and participated in operations with two warships that patrolled the Arabian Gulf, Indian Ocean, Gulf of Aden, Red Sea and the Suez Canal.
In a statement to Al Jazeera, the Bahrain-based Combined Maritime Forces (CMF) - the over-arching organisation of which the CTF is a part - confirmed that Pakistan is no longer participating with ships in the task force.
"Currently, Pakistan provides experienced naval personnel, very knowledgeable in areas such as operating in the Indian Ocean," CMF spokesperson Wendy Wheatley said.
"The current constituents of CTF 151 does not include Pakistan, however, a new team of nations take over every 4-6 months," she added.
"Participation remains purely voluntary and no nation is asked to carry out any duty that it is unwilling to conduct."
ROCKY RELATIONS -
Distancing itself from CTF gives Pakistan a chance to carry out an independent Regional Maritime Security Patrol (RMSP) from the Gulf of Aden to the Gulf of Oman, and from the Strait of Hormuz to the Maldivian waters, a Pakistani military official said.
Pakistan, which shares a border with Iran and also has a major trade relationship with China, has had a rocky relationship with the administration of US President Donald Trump.
Responding to the end of Pakistani participation in the anti-piracy task force, Pakistani military officials said the country has to guard its own interests in the western India Ocean.
"The objective of the RMSP initiative by Pakistan Navy is to maintain presence along critical areas to fulfil international obligations for maritime security and safeguard national shipping while observing freedom of navigation across high seas," the official said.
Pakistani security analysts believe Islamabad's warming relations with Iran's military, as well as security agreements with China could be cause for concern in Washington and Riyadh.