Japan's top convenience store chain operator Seven-Eleven Japan Co. on Thursday started trials of shorter opening hours, in a move toward reviewing its long-held policy of operating stores 24 hours a day, amid a serious shortage of labor.

In the pilot project, Seven-Eleven will open 10 stores it directly operates according to one of three time frames -- from 5 a.m. to 1 a.m. the following day, 7 a.m. to 11 p.m., and 6 a.m. to midnight, to see any changes in sales and customer traffic compared with 24-hour operation.

It said one of the 10 stores is in Tokyo but did not disclose the locations of the other nine or which time frame will be tested in each store.

The Tokyo-based company has said it does not intend to change its policy of 24/7 operation in principle and whether shorter opening hours are introduced at its franchise stores will depend on the results of the trials.

Seven-Eleven decided to conduct the trials after a group of convenience store owners called on Feb. 27 for a review of its policy requiring all owners to keep their stores open 24 hours a day, citing difficulties securing staff.

Mitoshi Matsumoto, who owns a Seven-Eleven store in Higashiosaka, western Japan, started closing his store overnight from Feb. 1 but was accused by the chain operator of violating its contract. Matsumoto said he was asked to cancel the contract or pay a penalty if he did not return to 24/7 operation.

The chain, which started 24/7 business hours at convenience stores in 1975, operates around 21,000 of the over 55,000 such stores in Japan.

Around 96 percent of Seven-Eleven stores open 24/7, except for those in locations such as office buildings and train stations, according to the company.

The company has not made public when it will end the pilot program.

It introduced 24-hour operation not only for customer convenience but because its logistics are built on the model, including restocking shelves during late-night hours.

The labor crunch in Japan has prompted other retailers and restaurant operators to review 24/7 operations.

Convenience store operator FamilyMart Co. has also tested shorter opening hours, while rival Lawson Inc. already allows franchise stores to cut operating hours.

Royal Holdings Co. ended 24-hour operation at all Royal Host restaurants in January 2017. McDonald's Holdings Company (Japan) Ltd. is also proceeding with a review of around-the-clock operations.

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Japan convenience store chain reviews 24-7 opening due to labor shortage