WASHINGTON — President Donald Trump is canceling pay raises due in January for most civilian federal employees, he informed Congress on Thursday, citing budget constraints. But the workers still could see a slightly smaller boost in their pay under a proposal lawmakers are considering.

Trump said he was nixing a 2.1 percent across-the-board raise for most workers as well as separate locality pay increases averaging 25.7 percent.

“We must maintain efforts to put our Nation on a fiscally sustainable course, and Federal agency budgets cannot sustain such increases,” said Trump. The president last year signed a package of tax cuts that is forecast to add about $1.5 trillion to federal deficits over 10 years.

Trump cited the “significant” cost of employing federal workers as justification for denying the pay increases, and called for federal worker pay to be based on performance and structured toward recruiting, retaining and rewarding “high-performing Federal employees and those with critical skill sets.”

His announcement came as the country heads into the Labor Day holiday weekend.

Democrats immediately criticized the move, citing the tax cuts Trump signed into law last December. That law provided steep tax cuts for corporations and the wealthiest Americans, and more modest reductions for middle- and low-income individuals and families.

“Trump has delivered yet another slap in the face to American workers,” said Democratic National Committee Chairman Tom Perez.

Under the law, the 2.1 percent raise takes effect automatically unless the president and Congress act to change it. Congress is currently debating a proposal for a slightly lower, 1.9 percent across-the-board raise to be included in a funding bill that would require Trump’s signature to keep most government functions operating past September.

Unions representing the 2 million-member federal workforce urged Congress to pass the 1.9 percent pay raise.

“President Trump’s plan to freeze wages for these patriotic workers next year ignores the fact that they are worse off today financially than they were at the start of the decade,” said J. David Cox Sr., president of the American Federation of Government Employees, which represents some 700,000 federal workers.

“They have already endured years of little to no increases and their paychecks cannot stretch any further as education, health care costs, gas and other goods continue to get more expensive,” added Tim Reardon, national president of the National Treasury Employees Union.

Cox said federal worker pay and benefits have been cut by more than $200 billion since 2011.