WASHINGTON (From news reports) -- Textbook publishers Cengage Learning Holdings and McGraw-Hill Education, who announced last year that they would merge, have extended their merger agreement to May 1, the companies said on Wednesday, as some countries are still reviewing the deal.

The proposed merger, which was announced in May 2019, had been set to expire on Feb. 1.

The deal has prompted criticism because it reduces the number of major textbook publishers from four to three.

Sources close to the two companies say their combined market share is 30% at most.

That differs from figures by market research firm Simba Information, which put Cengage's share at 22% and Apollo Global Management-owned (APO.N) McGraw-Hill at 21%, behind leader Pearson with 40% of the market by revenue, and ahead of Wiley at 7%.

The Justice Department, which is reviewing the deal to ensure it complies with U.S. antitrust law, has not yet made a decision.

"Conversations with the Department of Justice are ongoing. Until the merger is completed, we remain separate companies and operate as independent businesses," said a spokeswoman for the two companies.

In mid-January, Britain's Competition and Markets Authority asked for comments on the proposed transaction and whether it would lead to "a substantial lessening of competition."

And in December, the Australian Competition and Consumer Commission said that it had "raised preliminary competition concerns" about the deal.