Waste Management on Monday made an unsolicited offer to buy disposal company Republic Services Inc. for $6.19 billion in cash, aiming to block its biggest rivals from teaming up against the nation’s largest garbage hauler.

The moved countered a deal announced in June in which the third-largest waste hauler, Republic, said it would buy Allied Waste Industries, the second-largest, in a stock combination worth $6.07 billion at the time.

But that deal’s worth had declined along with Republic’s share price and was valued at about $5.43 billion, $12.56 a share, as of Friday’s close.

“We are confident that after you have considered our proposal you will agree that its terms are significantly more attractive to your stockholders than the Allied transaction,” David Steiner, chief executive of Houston-based Waste Management, wrote Monday to James O’Connor, Republic’s chairman and chief executive.

Waste Management’s per share offer represented a 22 percent premium to Fort Lauderdale, Fla.-based Republic Services closing stock price of $27.90 on Friday. On Monday, shares of Republic closed up nearly 14 percent at $31.76.

Republic said its board of directors will review the $34 per share offer from Waste Management and respond “in due course.”

Steiner told analysts in a conference call Monday that the Republic-Allied deal spurred Waste Management to make its offer.

“We did not go out looking for this deal and did not contemplate making an unsolicited offer for Republic, but when Republic was put into play as result of their agreement with Allied, we were presented with an opportunity we felt we could not ignore,” he said.

Steiner said the move does not signal a return to a strategy of growth through acquisition.

“Once we close this transaction we will spend all of our time and efforts to ensure a smooth integration,” he said. “We will not look to make any other significant acquisitions.”

Waste Management said it was looking forward to a prompt decision on its offer and cooperation from Republic’s board in presenting the deal to shareholders.

“The combination is highly complementary,” Waste Management said. It expected that the pairing up of the companies would give each more operating efficiency along its collection routes, among other advantages.

If the deal ultimately goes through, Waste Management’s share of the industry would rise to 30 percent from 24 percent now, said Stewart Scharf, an equity analyst at Standard & Poor’s in New York.

Looking ahead, Waste Management sees the deal boosting its earnings in the first year and provide cost savings of at least $150 million.

Waste Management believes all financing needed to complete the deal with be available on satisfactory terms it said.

It also expects to maintain investment grade status, due in part to rating agencies’ favorable view of the solid waste industry and Waste Management’s “leading role in the industry” and “enhanced scale that would result from the merger.”

However, Moody’s Investors Service placed its senior unsecured debt rating of Waste Management — “Baa3” — on review for possible downgrade.

“The proposed transaction would require significant debt financing to complete and would likely result in credit metrics at WMI that are more consistent with a speculative grade rating,” said Moody’s Analyst Jonathan Root.

Goldman Sachs analyst David Feinberg said in a note to clients Monday that Waste Management’s offer appears aimed at a clause within the Allied Waste-Republic Services merger agreement whereby management must consider “superior offers.”

Feinberg expected the announcement to weigh on Waste Management’s shares, but said the company’s positive second-quarter earnings outlook Monday gives him confidence in his “Conviction Buy” rating.

Shares of Waste Management closed down $2.12, or 5.8 percent, at $34.49 Monday.

Meanwhile, a spokesman for Allied Waste Industries in Phoenix, did not comment specifically on Waste Management’s bid for Republic Services. In a statement, he said Republic’s proposed stock deal for Allied creates “significant long-term value for the shareholders of both companies.”

Share of Allied Waste fell 20 cents, or 1.7 percent, to $11.79, on Monday. In the June deal, Republic had agreed to pay Allied shareholders .45 worth of a Republic share for each Allied share they held.

Going forward, Waste Management CEO Steiner said in an interview that his company will divest assets if required to do so by the U.S. Department of Justice.

Identifying which assets would not occur until after Waste Management and Republic meet to discuss the deal, he said.

Revenue last year for Waste Management was $13.31 billion, and $6.01 billion for Allied. Republic’s revenue stood at $3.18 billion.

Waste Management also said Monday it expects second-quarter earnings to beat Wall Street’s expectations.

The company predicted a profit of 64 cents per share, or an adjusted profit of 61 to 62 cents per share. It predicts sales will rise 4 percent to $3.49 billion.

Analysts polled by Thomson Financial, on average, expect earnings of 58 cents per share on revenue of $3.42 billion.

Waste management will announce second-quarter results on July 29.