Four Fairfax County delegates are urging Gov. Bob Mc­Don­nell (R) to veto a bill mandating that elementary and middle schools devote 150 minutes to physical education each week.

In a letter sent earlier this week, the four Republicans — Dels. Dave Albo , Barbara Comstock, Tim Hugo and Tom Rust — call the bill an “unfunded mandate” that would, according to Fairfax officials, cost the county $18 to $24 million and “crowd out other mandates and accountability requirements in academics.”

“In science and math, we need to be increasing our time on task, not decreasing it,” they write. “This bill would have the opposite impact and set us back academically.”

The letter specifically praises McDonnell’s wife Maureen, along with Michelle Obama, for embracing the cause of ending childhood obesity, which bill supporters say motivated the legislation.

But they write that the issue is better addressed though the private sector and public education than a “one size fits all mandate to our schools.”

All four of the delegates voted against the bill in the General Assembly, so their continued opposition is not surprising. But their letter, following a similar missive from Fairfax County, ratchets up the pressure on Mc­Don­nell to veto the measure.

He has not yet indicated whether he intends to sign the bill into law.