KARACHI, Pakistan, July 20 (Reuters) - Fuel pump operators across Pakistan are to hold a nationwide strike on July 22 in a bid to secure larger margins amid an inflation crisis, the Pakistan Petroleum Dealers Association said on Thursday.

"We will shut down all petrol pumps across Pakistan on July 22, 6 p.m.," said the association, which says it has more than 10,000 members.

In a statement it said interest rates and inflation have hit operators' businesses and called for the dealership margin to be increased. It said sales have slumped by 30% due to Iranian fuel being smuggled into the country.

"Around 8,000-9,000 (operators) ... represented by us, will be shut on July 22," Abdul Sami Khan, chairman of the association, told Reuters.

The South Asian country is dealing with a weakening currency and a prolonged period of inflation with the national rate hitting 29.4% in June, down from a record high of 38% in May. (Reporting by Ariba Shahid in Karachi; Editing by Conor Humphries)