Spending by independent expenditure groups in the 37th Senate district is growing, as a group backed by charter school and education reform supporters is spending $543,887 on a TV and radio campaign in the Westchester County seat.

The filing posted by the Board of Elections on Monday shows the money is being spent by New Yorkers For A Balanced Albany, a group linked to StudentsFirstNew York.

Democrats and teachers unions have previously slammed the involvement by the group in the race.

Meanwhile, Balance New York, a Republican-aligned group that has been funded by the Washington-based Republican State Leadership Committee, filed that it will spend $189,179 on a media buy in the district.

The money is being spent to boost Republican Julie Killian who faces Democratic candidate Shelley Mayer in the April 24 race. The special election is one of 11 that is being decided that day, but the suburban race is considered key for Democratic control of the state Senate in order to trigger a potential unity agreement by this spring.