KUNDUZ, Afghanistan — Rahimullah served in the Afghan Army for two years, deployed to the bloody front lines of the southern province of Helmand. When he quit, it was not because of the combat: It was when the Taliban went after his family back home, telling them that if he didn’t leave the army there would be a fine of one Kalashnikov rifle, seven cartridge magazines and $1,000 — or worse.

“My father called me to say the Taliban are demanding this,” said Mr. Rahimullah, 30, who now lives back in the eastern province of Kunar with his family. “I left the army, and some other of my friends left, too. We didn’t have the money to pay them. We had joined the army from poverty.”

Such demands are another way that the Taliban have been able to keep pressure on the Afghan Army, which was already struggling with record casualties and attrition. As the insurgents have made inroads in eastern and northern Afghanistan — long the most important recruiting grounds for the army — they are directly threatening the military’s ability to replenish its dwindling ranks.