ETA has stopped extorting money from businesses with threats of violent revenge since declaring a ceasefire January 10 in its battle for Basque independence, firms say.
Extortion has until now been the biggest source of financing for ETA, whose campaign of instilling fear by shootings and bombings has claimed the lives of 829 people over more than four decades.
The head of one small business in Spain's Basque Country, who declined to give more than his first name, Inaki, said he received his last letter demanding 300,000 euros ($412,000) in September.
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Written in Basque and Spanish, it was signed "Euskadi ta Askatasuna," or Basque Country and Freedom (ETA).
It was his fourth written demand, of which the first four years earlier had requested payment of 120,000 euros.
He has never paid.
"There were threats saying that for those who don't agree to pay, their families and possessions could be the target of revenge," said the business chief, aged about 60.
"They could put a bomb in your car, or target the factory."
Inaki said he has been "calmer" since the ceasefire but remains cautious: "I still avoid some districts, check occasionally under the car" to see if there is a bomb.
"For now, I don't think the letters will come back. But I would like to see what happens. I am calmer, but not completely," he said. "I think we are near the definitive end (of ETA) but I am still not entirely sure."
In the past weeks there have been none of the infamous letters demanding a "revolutionary tax" and marked with the ETA symbol of a serpent twisted around an axe, said Basque business federation Confebask.
Joseba Marcaida, president of the Zaitu federation in defence of people threatened by ETA, said no new extortion letter had been received since November 2010.
If confirmed it would be the first time ETA has halted extortion in recent history; the menacing letters continued throughout previous ceasefires declared in 1998-1999 and 2006-2007.
Each letter demands a precise sum, varying from several thousand euros to several hundred thousand euros, depending on the size of the targeted business, said ETA analyst Florencio Dominguez, chief editor of Vasco Press.
Much like a collection agency, it sends reminders with penalty fees for firms that fail to pay up, he said.
But for Mikel Buesa, specialist in terrorism financing at the Complutense University in Madrid, a pause of a few weeks does not prove the band has abandoned the practice.
The extortion letters were usually sent in waves, with pauses of several months in between, he said.
In 2010, extortion by mail appeared to intensify with increasingly large sums demanded, as if ETA was trying to redouble its efforts to rake in as much money as possible before the ceasefire, he said.
According to Buesa, only 10-20 percent of threatened businesses pay up, and they often do so in instalments over several years.
Money already raised in recent years, which he estimated at 3.5 million euros in 2009 and 5.1 million euros in 2010, would continue to finance ETA for months to come, he said.
Fear inspired by ETA had eased, with its last attack dating to August 2009, Buesa said. But that does not mean that business chiefs who have been threatened in the past feel they can relax.
"The extortion process is subtle and the entrepreneurs know that," Buesa said.
"They are not threatened with death but with having their lives made impossible and with suffering economic losses," for example by arson attacks on their businesses, he said.
