Taking his turn at the microphone for the Republican weekly radio address Saturday, Rep. Jerry Weller of Illinois broadcast the news that eliminating the so-called marriage tax penalty will be his party’s top priority this year. Just as it was last year and for every year back to 1994.

“Republicans believe it is wrong and unfair that today’s tax code imposes higher taxes on married working couples,” said Rep. Weller. “In fact, an average married working couple pays almost $1,400 more in taxes than an identical couple living together outside of marriage.”

In actual fact, the congressman tells only half the story. Make that 42 percent of the story. For that is the percentage of joint filers who paid an average marriage penalty of $1,400 last year. Some 51 percent got a marriage bonus averaging $1,300.

That statistic should be enough to refute the tiresome assertion that the marriage tax is the result of some anti-family conspiracy. It hasn’t been enough, and that is why the marriage tax is in year five of top priority status and holding.

There is no deliberate marriage penalty or bonus, but there is a disparity that results when a tax code tries to be progressive (those who earn the most pay higher rates) while it fluctuates between making the individual and the family the taxation entity.

Because of the principle of progressivity, two spouses with near equal incomes pay more than they would as singles. The wider the gap between the spouses’ incomes, the greater the bonus; the joint tax on two incomes of $50,000 each is more than it is on incomes of $30,000 and $70,000. The marriage penalty/bonus is nothing new. It dates back to 1948, when Congress changed the tax code to average the total income between spouses and it’s been tinkered with twice since then. It’s just becoming more of a problem as more women enter the workforce and as the gender gap in incomes narrows.

In addition, the Census Bureau reports that the number of unmarried adults of the opposite sex living together has increased from 523,000 in 1970 to nearly 4 million today. A lot more Americans look like married folks but don’t pay taxes like them. And this may not unrelated to the tax code: studies by the highly regarded National Policy Institute strongly suggest a pre-nuptial visit to a CPA may well be guiding some marriage plans, especially for lovebirds with near-equal incomes. Many things influence human behavior; tax laws included.

The marriage penalty/bonus is but one of the more visible flaws in a bloated tax code that grows more incomprehensible every time Congress fiddles with it. For five years, the GOP has tried to use it for political advantage. Now it’s time to fix it.