Five days after boosting its unsolicited takeover bid for Tribune Publishing Co. by 22 percent, USA Today owner Gannett is urging Tribune shareholders to reject the company’s slate of nominees to sit on its board.

In a letter Friday to Tribune shareholders, Gannett Co. said Tribune’s board “is disregarding your interests by preventing you from realizing superior and certain cash value for your shares.” It asks the shareholders to withhold their votes for Tribune’s eight director nominees on proxy cards mailed in advance of Tribune’s annual meeting on June 2.

Gannett on Monday raised its bid to $15 per Tribune share from $12.25 offered earlier for the owner of the Los Angeles Times, Chicago Tribune and other newspapers, after Tribune adopted a “poison pill” plan to thwart the offer.