Plastics manufacturer A. Schulman Inc. on Monday slashed its earnings guidance for the year as quality issues from an acquisition continue to batter results.

The company now anticipates adjusted earnings for 2016 of $2.40 to $2.45 a share, compared with a previous outlook for $2.80 to $2.85 a share.

Shares in the company, which have fallen 4% over the past three months, lost another 12% premarket to $24.56.

Schulman discovered quality reporting issues affecting certain product lines at two former HGGC Citadel Plastics Holdings manufacturing facilities that were once part of Lucent Polymers, which was acquired by Schulman in March 2015.

In January, the company reported its profit almost halved in its first quarter as costs tied to an investigation weighed on the results, which sharply missed Wall Street expectations.

On Monday, Chief Executive Bernard Rzepka said the company is "extremely disappointed with our preliminary view of second quarter," which is expected to yield adjusted earnings of about 25 cents to 30 cents a share—sharply below analyst estimates for 48 cents a share, according to Thomson Reuters.

Mr. Rzepka said the business teams have been focused on correcting the previously disclosed Lucent quality matter, diverting them away from planned growth initiatives. He said the company expects the financial impact from Lucent to continue into the second half. He also said both the Citadel and legacy businesses experienced weakness driven by low oil prices, which impacted sales volumes.

"Although the weakness will continue until the global oil environment recovers, we believe that the demand for our products has stabilized albeit at a reduced level," Mr. Rzepka said.

He also pointed to continuing global economic slowdown, and said additional cost cuts weren't enough to offset the above factors.

The Ohio company, which does most of its business abroad and has been hit hard by falling demand in Europe, has also been hurt by a stronger U.S. dollar.

Because of the Lucent quality issue and the current oil price climate, the company doesn't anticipate the Citadel acquisition to be accretive until fiscal 2017.

A. Schulman will release its second-quarter results after the market closes on April 5 and "provide additional insight into the factors impacting its near-term results, an update on Lucent and the company's legal options related to the Citadel acquisition."

Write to Anne Steele at Anne.Steele@wsj.com

(END) Dow Jones Newswires

March 14, 2016 10:25 ET (14:25 GMT)