U.S. Sen. Scott Brown is criticizing President Barack Obama for bypassing Congress and moving to ease enforcement of the nation’s immigration laws.

Brown said Friday that Obama’s action, which gives hundreds of thousands of illegal immigrants a chance to stay in the country and work, is too broad and would set off a new wave of illegal immigration.

“It’s also unfair to the millions of immigrants who are playing by the rules and waiting patiently to enter the country legally,’’ Brown said in a statement. “We welcome those who seek a better life in America, but we are also a nation of laws that have to be respected.’’

The Massachusetts Republican said he would be open to letting young people who have joined the military obtain citizenship, however, out of recognition for their service to the country.

Brown’s Democratic challenger, Elizabeth Warren, praised Obama’s plan, which protects illegal immigrants from deportation if they arrived in the United States before they turned 16.

“These young people did nothing wrong, they were brought to this country by their parents,’’ Warren said in a statement. “They have gone to school here or served in the military, and they should be able to continue living and working here.’’

The policy change will affect as many as 800,000 immigrants who have lived in fear of deportation.

The order bypasses Congress and partially achieves the goals of the DREAM Act, legislation that would establish a path toward citizenship for young people who came to the United States illegally but who attend college or join the military.

In 2010, Brown opposed the legislation.

“I think it’s a backdoor amnesty and I’m not in favor of it,’’ Brown said at the time, despite coming under months of pressure from advocates and educators, including Harvard University President Drew Gilpin Faust.

Warren, who teaches at Harvard Law School, was quick to note Brown’s opposition to the bill.