The government has approved the sale of more than 200 school playing fields in recent years, according to a new report.
Research by the GMB union suggests that, since May 2010, a total of 215 school playing fields have been sold across England.
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Reasons for the sales include school closures or mergers, drainage problems, building affordable housing, or investment in new facilities.
GMB official Francis Duku said: "The government has cut education funding to such an extent [that] schools are being forced to flog their playing fields to make ends meet.
"It's pretty hypocritical for Conservative ministers to push through the sell-offs they once condemned.
"At a time when the nation is celebrating the success of both the men's and women's national football teams, it's a disgrace that fewer schoolchildren will have anywhere to play.
"This shortsighted sell-off of the family silver is going to have serious health implications for generations to come.
"We need support for the semi-professional game and proper funding for the grassroots football which will produce the next generation of England stars."
The Department for Education has been contacted for comment.