The law was passed in the wake of the Hillsborough disaster when 96 supporters were crushed to death and many more injured due to over-crowding at an FA Cup semi-final between Liverpool and Nottingham Forest in 1989.
Standing sections in the top two English divisions were subsequently removed and stadiums converted into all-seater arenas.
A photo on Twitter showed a seat at Sunderland's Stadium of Light taped up with the sign: "This season card has been suspended due to persistent standing."
Sunderland said in a statement on their website that 38 supporters have been ejected for standing this season.
"We certainly don't wish to spoil the enjoyment of any supporters... but we also have legal obligations that we must be seen to be adhering to," said Paul Weir, head of safety and security at Sunderland.
The club said they could be forced to close areas where standing persists, although they are keen to avoid such a measure.
A number of campaigns have been launched to try to change the law on standing, most notably by the Football Supporters' Federation.
A United Kingdom House of Commons note published earlier this month said: "The Government has said that it will keep matters under review, but that there is no 'compelling case' for a change to the current rules."
Standing is allowed in many other European top flights.
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