A couple of hundred Palestinian refugees protested Tuesday in the streets of Beirut against Lebanon's labour ministry cracking down on businesses employing foreign workers without a permit.
They and dozens of demonstrators in Palestinian refugee camps in the capital, as well as the south and east of the country, denounced the move as "unfair".
Last month, the ministry gave companies a one-month deadline to acquire the necessary work permits.
After the grace period expired last week, it started inspections, closing down non-compliant establishments and issuing others with warnings.
Critics have said the measure essentially targets Syrians who have fled the war next door, but Palestinian refugees living in Lebanon also fear they will be hit.
In Beirut, security forces prevented the protesters from reaching parliament, where this year's much delayed state budget was under discussion.
Palestinians in Lebanon are exempt from paying for work permits, the UN refugee agency says.
But Palestinian business owners must still register and pay a quarter of the standard fee.
Labour Minister Camille Abousleiman denied the inspections had overwhelmingly affected Palestinians.
"Of the 550 violations registered since last Wednesday, only two concerned large companies owned by Palestinians," he said.
"The Palestinian reaction is incomprehensible," the minister said.
The Palestinian ambassador in Beirut, Ashraf Dabbour, on Monday called on the Lebanese government to exempt Palestinians from these measures.
Palestinian movement Hamas called for "the immediate end to all closures".
Azzam al-Ahmad, from the Palestine Liberation Organisation, discussed the measures with Lebanese officials, saying they went against Lebanese-Palestinian efforts "to organise the residency, work and rights of Palestinian refugees in Lebanon".
Around 174,000 Palestinian refugees live in 12 camps across the country, a one-off government census said in 2017.
In 2010, Lebanon's parliament revoked a ban that had barred them from tens of professions for years, restricting them to jobs in fields such as construction and farming.
But Palestinians are still not permitted to work in professions reserved for Lebanese citizens such as medicine, law, the army, and police.
Palestinians began taking refuge in Lebanon with the creation of Israel in 1948, setting up camps that have since transformed into bustling, urban districts.
Their presence has been controversial, with many blaming them for the start of Lebanon's 1975-1990 civil war.
Lebanon says it hosts around 1.5 million Syrians, after they fled the eight-year conflict at home, who have been accused of sparking a series of economic woes in the country.