The Office of Fair Trading has delayed Travis Perkins' £533m takeover of plumbing and heating supplier BSS by a further month.
The builders merchants announced the bid in June, but it was called in by the OFT on 19 July.
The deal would see Travis Perkins move ahead of Wolseley as the UK’s largest plumbing and heating retail business.
The OFT has now indicated that its decision on the proposed acquisition will not be made until 19 October.
It is considering whether the takeover would constitute a merger situation under the provisions of the Enterprise Act 2002, in which case it would be referred to the Competition Commission.