Transport for London (TfL) has defended its decision to slash £1.5m funding for the London Transport Museum by 2015 following protests by the Transport Salaried Staffs’ Association (TSSA) union.

In a letter to the Guardian, TfL’s managing director of marketing and communications, Vernon Everitt, said savings must be made “to protect essential frontline transport services and investment. Our contribution to the museum must reduce to more sustainable levels.”

TfL received a funding cut of £2.2bn over four years from the Department for Transport as part of the Comprehensive Spending Review in 2010.

Everitt also highlighted the “need to align entry-salary levels at the museum with those paid elsewhere in the cultural and museum sector”. Sam Mullins, director of the London Transport Museum, said salaries started at about £23,000, in line with TfL pay grades.

“We’d like to bring these into line with our industry for new starters,” he added. Mullins stressed that the museum offered a “very generous package” for entry-level curatorial and administrative staff compared with national museums.

TSSA general secretary Manuel Cortes had expressed concerns about the TfL spending squeeze in a letter to the Guardian last month.

Cortes urged TfL to reinstate the £1.5m cut, stressing that seven posts were set to be abolished at the museum and that the school visits programme, a transport safety scheme, was in jeopardy.

Mullins said, however, that the education project was not under threat, while the seven posts in question referred to the termination of Renaissance contract roles.

Earlier this year the museum, a charitable foundation, failed in its bid to become a major partner museum under ACE’s reworked Renaissance scheme. Transitional funding of £597,000 was subsequently awarded by ACE to the museum. The museum’s operating budget for 2012-13 is £9.6m.