Senate Minority Leader Charles E. Schumer on Friday likened the House GOP’s newly unveiled tax legislation to a “dead fish” and said it represents a “betrayal” to middle class families throughout the country.

“Put simply, the bill is like a dead fish,” Mr. Schumer, New York Democrat, said on a conference call with reporters. “The more it hangs out in the sunlight, the stinkier it gets.”

“The more people learn about this bill, the less they’re going to like it,” he said.

House Republicans have pitched their massive tax code rewrite as a boon to the middle class, saying that an average family can expect to see tax savings of nearly $1,200.

In addition to lower individual tax rates, the GOP says an expanded standard deduction and an enhanced family credit, among other provisions, will make up for the loss of other popular breaks, like the ability for people to deduct the state and local income taxes they pay.

But Mr. Schumer pointed out that the new family credit sunsets in 2022, and said the plan also axes a $4,050 personal exemption taxpayers can take for themselves and certain dependents.

“It’s a pure betrayal of the middle-class families the president promised to stand up for,” he said.

Earlier in the day, House Ways and Means Committee Chairman Kevin Brady acknowledged that certain deductions presented “tough choices” for tax writers but said families across the board would ultimately benefit from the plan.

“At every level, there is tax relief,” said Mr. Brady, Texas Republican.

Mr. Brady, who has two adopted children, acknowledged that an adoption tax credit the plan zeroes out is “near and dear to me.”

“These are tough calls,” he said at a Politico event. “The call is this: do we want a tax code that has special provisions you may use once in your life, or do we want a tax code that lowers rates and you get help every year of your life?”