restriction on his client working

[suprunp]

Rooney told the panel that maintaining the restriction on his client working would be "disproportionate and devastating" for her professional reputation and her financial situation.
(The Guardian.
"Stepping Hill hospital nurse allowed to work under 'conditions'")

What role does 'working' play here from a grammatical point of view?

Thanks.

[billmcd]

Rooney told the panel that maintaining the restriction on his client working would be "disproportionate and devastating" for her professional reputation and her financial situation.
(The Guardian.
"Stepping Hill hospital nurse allowed to work under 'conditions'")

What role does 'working' play here from a grammatical point of view?

Thanks.

Gerund, object of the preposition "on".