A co-worker has a L1A Visa and will be living in the US for all of 2008. He is married with children and would like to complete a Form W4 as married with 2 addition exemptions. Does IRS regulations prohibit him from doing so and requiring his employer to deduct his taxes as single? Help appreciated!

If he is in the U.S. EVERY day in 2008, he will file as a resident alien.

In that case, he can file his W-4 as Married with two additional exemptions.