Patton Boggs is putting a tighter squeeze on clients to pay their bills on time as the firm continues cost-­cutting measures and entertains a potential merger. At the same time, the firm is suing to collect unpaid bills, filing the latest lawsuit this month in a series of fee disputes in Washington-area courts.

Big law firms don’t often take fee fights to court. But since June, Patton Boggs has filed four lawsuits in District of Columbia and Virginia courts seeking nearly $2 million. The firm’s general counsel, Charles Talisman, acknowledged it was rare for a law firm to sue a client.