Yemen's Houthi rebels are shutting down organisers of Hajj and Umrah pilgrimages who refuse to pay a new fee imposed on them, according to staff at the affected agencies.
At least 18 travel agencies were shut down in the rebel-held capital, Sanaa, a manager at one of the agencies told Al Arabiya.
The Houthis have also shut down agencies in other areas under their control and are tracking down their owners, the Saudi broadcaster reported on its website.
A manager at another travel agency in Sanaa said the clampdown came after the rebels' religious ministry issued a list of officially approved Hajj and Umrah booking agencies. These agencies were then told to pay a fee for every pilgrim who booked through them as "operational expenses" for the ministry, the manager told Al Arabiya.
Both managers declined to be named over fears for their safety.
The Hajj pilgrimage this year is likely to begin around August 19. Last year the Iran-backed rebels to stop Yemenis from travelling to Saudi Arabia for the pilgrimage by confiscating their passports and blocking their departure.
Saudi Arabia leads an Arab military coalition that has been fighting the Iran-backed rebels since March 2015. Yemeni forces backed by the coalition, which intervened in the war at the request of President Abdrabu Mansur Hadi, have liberated most of southern Yemen and are poised to retake the key port of Hodeidah on the Red Sea coast.
The Houthis have been accused of using their control of the port, which handles the bulk of Yemen's food and humanitarian aid imports, to control the distribution of supplies and raise funds.
Alastair Burt, Britain's minister for the Middle East, told parliament recently that the rebels "take taxes from good that come in, in order to finance themselves, enrich themselves".
The Saudi ambassador to Yemen, Mohammed Al Jabir, told a conference in Riyadh last month that the Houthis "have impeded the the delivery of humanitarian aid to Yemen".
Mr Al Jabir also accused the rebels of looting funds from Yemen's central bank, which used to be based in Sanaa but was relocated to Aden, the interim capital, on the orders of President Hadi.