The US Securities and Exchange Commission said Monday that it has sued four former Nortel Networks executives, accusing them of manipulating earnings to meet internal targets and Wall Street expectations.

The investor protection agency said in a statement that it has charged former chief executive Frank Dunn, former chief financial officer Douglas Beatty, former controller Michael Gollogly and former assistant controller MaryAnne Pahapill.

The executives repeatedly engaged in accounting fraud between 2000 and 2004, the SEC said in a statement.

“The fraudulent conduct at issue here was egregious and long-running,” said Linda Thomsen, enforcement chief at the SEC. “Each of the defendants betrayed Nortel’s investors and their misconduct gave rise to billions of dollars in shareholder losses,” she added in a statement.