WASHINGTON — A lack of unanimity in both political parties toward President Barack Obama’s sudden move to re-establish ties with Cuba complicates any congressional effort to scuttle the most significant change in U.S. policy toward the communist island in 50-plus years.

His initiative faces some strong resistance among lawmakers, with criticism coming mostly from Republicans, who say the new policy rewards Cuba’s decades-long policies of repression, human rights abuses and aggression. Some prominent Democrats voiced opposition, too.

Opponents spoke of holding up money to set up a full-service U.S. embassy in Havana, blocking Obama’s nominee as ambassador to Cuba or other such steps. But even if they were to pass sweeping legislation to stop what Obama wants to do, he could veto it and they are unlikely to muster the two-thirds majority to override a veto.

The GOP will control both the Senate and House come Jan. 6, but Republicans will face pressure from businesses and the farm industry — eyeing opportunities for commerce in Cuba — not to stand in the way of expanded ties.

The Chamber of Commerce spent heavily in the midterm elections, investing $35 million to elect business-minded, predominantly Republican lawmakers. Its president, Thomas J. Donohue, said Wednesday that Obama’s actions “will go a long way in allowing opportunities for free enterprise to flourish.”

The U.S. declared an embargo on most exports to Cuba in October 1960 and severed diplomatic relations in January 1961. Three months later Fidel Castro declared Cuba a socialist state — just a day before the doomed, U.S.-sponsored Bay of Pigs invasion meant to topple him. After the hard-line Castro became ill in 2006, his brother, Raul, took charge of the nation, fewer than 100 miles off the southern coast of Florida.

Now Obama says he will ease economic and travel restrictions on Cuba and work with Congress to end the trade embargo. This came after Cuba released American Alan Gross, who had been imprisoned for five years, and a Cuban who had spied for the U.S. In exchange, the U.S. freed three Cubans jailed in Florida.

Even if opponents were to pass sweeping legislation to stop what Obama wants to do, he could veto it and they are unlikely to muster the two-thirds majority to override a veto. Sen. Patrick Leahy, D-Vt., one of three lawmakers who flew to Cuba before dawn to escort Gross home, praised Obama’s move.

Leahy, the top Democrat on the committee that oversees foreign aid, said that over the years he’s heard members of Congress tell presidents, “Hang tough on Cuba and those Castros will be out of there any day now.”

“That was said to President Kennedy, President Johnson, President Nixon, President Ford, President Carter — you see what I’m driving at,” Leahy said. “The fact is they are there. The fact is, Cuba is still there.

“Let’s start finding out ways to at least work through our differences, embrace areas where we are alike.”

Another Democrat, New Jersey Sen. Bob Menendez, the outgoing chairman of the Senate Foreign Relations Committee, voiced opposition to the new Cuban policy.

Menendez, whose parents are Cuban immigrants, said Cuba is not going to reform just because Obama believes that if he extends his hand in peace, the Castro brothers suddenly will “unclench their fists.”

The No. 2 Democrat in the Senate, Dick Durbin of Illinois, said he understands the feelings of Cuban lawmakers who oppose Obama’s decision because of the pain associated with their families’ experiences in Cuba.

“But I think we have to step back as a nation and say if we’re ever going to move the Cuban people in the right direction of freedom, where they’re going to have democratic elections, then we’ve got to have a new relationship with Cuba,” Durbin said in Chicago.

Splits were evident on the Republican side, too.

Republican leaders in the House and Senate condemned Obama’s action, as did Sen. Marco Rubio, R-Fla., a Cuban-American and potential presidential candidate. Rubio said the new U.S. policy would give Cuba a needed economic lift — something “the Castro regime needs to become permanent fixtures in Cuba for generations to come.”

More telling for the outlook in the new Congress was the response of Sen. Bob Corker, R-Tenn., the incoming chairman of the Foreign Relations Committee, who was cautious but not critical of Obama’s action.

However, Sen. Jeff Flake, R-Ariz., who also went to Cuba to accompany Gross home, said Obama’s move should not be seen as a concession. “My sense is that most of my colleagues feel that we’re long past due” in moderating the U.S. stance on Cuba.

“Certainly the policy is right and good politics usually follow good policy,” Flake said.

As well as restoring diplomatic relations, Obama plans to ease travel restrictions to Cuba for family visits, government business and educational activities, while tourist travel remains banned. Only lawmakers can revoke the trade embargo, though, and that appears unlikely to happen soon.

Associated Press writers Donna Cassata and Tammy Webber in Chicago contributed to this report.