Lebanon, a country of some four million people, says it hosts at least 1.5 million Syrians on its soil after they fled the eight-year civil war next door, many living in informal settlements in the country's east.
Nearly a million are registered as refugees with the United Nations High Commissioner for Refugees.
To discourage any permanent settlement, Lebanese authorities gave Syrians living in the region of Arsal until July 1 to demolish shelters made of anything but timber and plastic sheeting.
Families have been forced to tear down any small cinderblock room they may have built, with the army stepping in to destroy at least 20 remaining hard shelters as the deadline passed on Monday.
"This crackdown on housing code violations should be seen for what it is, which is illegitimate pressure on Syrian refugees to leave Lebanon," Human Rights Watch (HRW) refugee rights director Bill Frelick said.
"Many of those affected have real reasons to fear returning to Syria, including arrests, torture and ill-treatment by Syrian intelligence branches," he said.
After several Russia-backed victories against rebels and jihadists since 2015, the Damascus regime controls around 60 percent of Syria's territory.
Young Syrian men in Lebanon have also told AFP they fear military conscription if they return.
Aids groups have estimated up to 15,000 people, including 7,500 children, to have been affected by the demolition order.
One family made to destroy their shelter last month told AFP they would not return to Syria as their Syrian home had been destroyed by war, leaving them instead to face another harsh winter in a tent.
Echoing similar warnings from other rights monitors, HRW said the demolitions were just one of several methods used to pressure Syrians into leaving Lebanon.
"They include ramped up arrests and deportations, closing of shops, and confiscation or destruction of unlicensed vehicles, on top of other long-standing restrictions, including curfews and evictions, and barriers to refugee education, legal residency, and work authorisation," Frelick said.
"Lebanon shouldn't create pressures that cumulatively coerce refugees to return involuntarily in conditions that are not conducive to a safe and dignified return," he said.
Lebanese politicians and part of the population have called for Syrian refugees to go home, blaming them for a string of economic woes in the country.
Syria's war has killed 370,000 people and displaced millions at home and abroad since it started in 2011 with a brutal crackdown on anti-government protests.
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