Labour MP Chris Bryant has labelled the prime minister's plans for married couples the "unmarried tax."
Writing in the Independent, he said: "This is bad policy and even worse politics.
"It is High Tory political theology from a distant era.
"It does nothing to channel public funds to where they are needed.
"The man who leaves his wife and children and marries again will get it, while the divorced wife with children soldiers on without, just because she does not remarry.
"it pretends to espouse family values, but it is offensively naïve to think anyone really marries (or indeed should marry) for £150 a year tax relief.
"So let’s call it what it really is, the “unmarried tax”, and make sure it follows the pasty tax, the bedroom tax and the charity tax into history."